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{"sheet":"Document_and_Entity_Informatio","index":0,"n_rows":18,"n_cols":5,"rows_kept":18,"cut":false,"hidden":false,"merged":[]}
["Document and Entity Information (USD $)","0 Months Ended","12 Months Ended"]
["In Millions, except Share data, unless otherwise specified","Mar. 01, 2015","Dec. 31, 2014","Mar. 01, 2015","Jun. 30, 2014"]
["Document and Entity Information"]
["Entity Registrant Name",null,"Esperion Therapeutics, Inc."]
["Entity Central Index Key",null,1434868]
["Document Type",null,"10-K"]
["Document Period End Date",null,"2014-12-31"]
["Amendment Flag",null,false]
["Current Fiscal Year End Date",null,{"$f":"--12-31","v":-19}]
["Entity Well-known Seasoned Issuer",null,"No"]
["Entity Voluntary Filers",null,"No"]
["Entity Current Reporting Status",null,"Yes"]
["Entity Filer Category",null,"Accelerated Filer"]
["Entity Public Float",null,null,null,244.4]
["Entity Common Stock, Shares Outstanding",null,null,20425860]
["Document Fiscal Year Focus",null,2014]
["Document Fiscal Period Focus",null,"FY"]
["Entity Listing, Par Value Per Share",1E-3]

{"sheet":"Condensed_Balance_Sheets","index":1,"n_rows":29,"n_cols":3,"rows_kept":29,"cut":false,"hidden":false,"merged":[[0,1,1,1],[0,2,1,2]]}
["Condensed Balance Sheets (USD $)","Dec. 31, 2014","Dec. 31, 2013"]
["In Thousands, unless otherwise specified"]
["Current assets:"]
["Cash and cash equivalents",85038,56537]
["Short-term investments",20803,3525]
["Prepaid clinical development costs",366,196]
["Other prepaid and current assets",560,362]
["Total current assets",106767,60620]
["Property and equipment, net",780,81]
["Intangible assets",56,56]
["Long-term investments",35741,17537]
["Total assets",143344,78294]
["Current liabilities:"]
["Accounts payable",2040,2232]
["Current portion of long-term debt",638]
["Accrued clinical development costs",1978,884]
["Other accrued liabilities",835,1087]
["Total current liabilities",5491,4203]
["Long-term debt, net of discount",4299]
["Total liabilities",9790,4203]
["Commitments and contingencies (Note 5)","  ","  "]
["Stockholders' equity:"]
["Preferred stock, $0.001 par value; 5,000,000 shares authorized and no shares issued or outstanding as of December 31, 2014 and December 31, 2013","  ","  "]
["Common stock, $0.001 par value; 120,000,000 shares authorized as of December 31, 2014 and December 31,2013; 20,352,876 shares issued 20,343,325 outstanding at December 31, 2014 and 15,357,413 shares issued and 15,340,710 outstanding at December 31, 2013",20,15]
["Additional paid-in capital",238031,142142]
["Accumulated other comprehensive loss",-59,-3]
["Accumulated deficit",-104438,-68063]
["Total stockholders' equity",133554,74091]
["Total liabilities and stockholders' equity",143344,78294]

{"sheet":"Condensed_Balance_Sheets_Paren","index":2,"n_rows":10,"n_cols":3,"rows_kept":10,"cut":false,"hidden":false,"merged":[]}
["Condensed Balance Sheets (Parenthetical) (USD $)","Dec. 31, 2014","Dec. 31, 2013"]
["Condensed Balance Sheets"]
["Preferred stock, par value (in dollars per share)",1E-3,1E-3]
["Preferred stock, shares authorized",5000000,5000000]
["Preferred stock, shares issued",0,0]
["Preferred stock, shares outstanding",0,0]
["Common stock, par value (in dollars per share)",1E-3,1E-3]
["Common stock, shares authorized",120000000,120000000]
["Common stock, shares issued",20352876,15357413]
["Common stock, shares outstanding",20343325,15340710]

{"sheet":"Condensed_Statements_of_Operat","index":3,"n_rows":16,"n_cols":4,"rows_kept":16,"cut":false,"hidden":false,"merged":[[0,1,0,3]]}
["Condensed Statements of Operations and Comprehensive Loss (USD $)","12 Months Ended"]
["In Thousands, except Share data, unless otherwise specified","Dec. 31, 2014","Dec. 31, 2013","Dec. 31, 2012"]
["Operating expenses:"]
["Research and development",25302,16014,7998]
["General and administrative",10922,6745,2206]
["Total operating expenses",36224,22759,10204]
["Loss from operations",-36224,-22759,-10204]
["Interest expense.",-270,-936,-1486]
["Change in fair value of warrant liability",null,-2587,32]
["Other income (expense), net",119,194,-84]
["Net loss",-36375,-26088,-11742]
["Net loss per common share (basic and diluted) (in dollars per share)",-2.2200000000000002,-3.31,-36.31]
["Weighted-average shares outstanding (basic and diluted)",16374102,7885921,323382]
["Other comprehensive loss:"]
["Unrealized loss on investments",-56,-3]
["Total comprehensive loss",-36431,-26091,-11742]

{"sheet":"Statements_of_Convertible_Pref","index":4,"n_rows":44,"n_cols":8,"rows_kept":44,"cut":false,"hidden":false,"merged":[[0,7,1,7],[0,1,1,1],[0,2,1,2],[0,3,1,3],[0,4,1,4],[0,5,1,5],[0,6,1,6]]}
["Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (USD $)","Common Stock.","Additional Paid-In Capital","Deficit Accumulated During the Development Stage","Accumulated Other Comprehensive Loss","Series A preferred stock","Series A-1 preferred stock","Total"]
["In Thousands, except Share data, unless otherwise specified"]
["Balance at Dec. 31, 2011",null,201,-30233,null,null,null,-30032]
["Balance at Dec. 31, 2011",{"$nulls":4},23975]
["Balance (in shares) at Dec. 31, 2011",307742]
["Increase (Decrease) in Stockholders' Equity"]
["Exercise of stock options",null,41,{"$nulls":4},41]
["Exercise of stock options (in shares)",38736]
["Beneficial conversion feature from issuance of convertible notes",null,288,{"$nulls":4},288]
["Stock-based compensation",null,80,{"$nulls":4},80]
["Net loss",null,null,-11742,null,null,null,-11742]
["Balance at Dec. 31, 2012",null,610,-41975,null,23975,null,-41365]
["Balance (in shares) at Dec. 31, 2012",346478]
["Increase (Decrease) in Temporary Equity"]
["Issuance of preferred stock in exchange for convertible promissory notes, net of issuance costs",{"$nulls":4},16623,7750]
["Issuance of preferred stock in exchange for convertible promissory notes, net of issuance costs (in shares)",{"$nulls":4},16623092,6750000]
["Issuance of Series A preferred stock, net of issuance costs",{"$nulls":4},16880]
["Issuance of Series A preferred stock, net of issuance costs (in shares)",{"$nulls":4},17000000]
["Preferred shares converted into common stock",9,65216,null,null,-57478,-7750,65225]
["Preferred shares converted into common stock (in shares)",9210999,null,null,null,-57598092,-6750000]
["Increase (Decrease) in Stockholders' Equity"]
["Early exercise of stock options and vesting of restricted stock",null,21,{"$nulls":4},21]
["Early exercise of stock options and vesting of restricted stock (in shares)",25765]
["Issuance of common stock from public offering, net of issuance costs",6,72188,{"$nulls":4},72194]
["Issuance of common stock from public offering, net of issuance costs (in shares)",5750000]
["Reclassification of warrants from liabilities to equity",null,2852,{"$nulls":4},2852]
["Exercise of stock options",null,28,{"$nulls":4},28]
["Exercise of stock options (in shares)",24171]
["Stock-based compensation",null,1227,{"$nulls":4},1227]
["Other comprehensive loss",null,null,null,-3,null,null,-3]
["Net loss",null,null,-26088,null,null,null,-26088]
["Balance at Dec. 31, 2013",15,142142,-68063,-3,null,null,74091]
["Balance (in shares) at Dec. 31, 2013",15357413,{"$nulls":5},15357413]
["Increase (Decrease) in Stockholders' Equity"]
["Early exercise of stock options and vesting of restricted stock",null,39,{"$nulls":4},39]
["Issuance of common stock from public offering, net of issuance costs",5,91620,{"$nulls":4},91625]
["Issuance of common stock from public offering, net of issuance costs (in shares)",4887500]
["Issued warrants in connection with debt issuance",null,78,{"$nulls":4},78]
["Exercise of stock options",null,473,{"$nulls":4},473]
["Exercise of stock options (in shares)",107963,{"$nulls":5},107963]
["Stock-based compensation",null,3679,{"$nulls":4},3679]
["Other comprehensive loss",null,null,null,-56,null,null,-56]
["Net loss",null,null,-36375,null,null,null,-36375]
["Balance at Dec. 31, 2014",20,238031,-104438,-59,null,null,133554]

{"sheet":"Statements_of_Convertible_Pref1","index":5,"n_rows":8,"n_cols":3,"rows_kept":8,"cut":false,"hidden":false,"merged":[[0,1,0,2]]}
["Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) (USD $)","12 Months Ended"]
["In Thousands, unless otherwise specified","Dec. 31, 2013","Dec. 31, 2014"]
["Series A preferred stock"]
["Payments of Stock Issuance Costs",-120]
["Series A-1 preferred stock"]
["Payments of Stock Issuance Costs",53]
["Common Stock."]
["Payments of Stock Issuance Costs",2671,260]

{"sheet":"Condensed_Statements_of_Cash_F","index":6,"n_rows":43,"n_cols":4,"rows_kept":43,"cut":false,"hidden":false,"merged":[[0,1,0,3]]}
["Condensed Statements of Cash Flows (USD $)","12 Months Ended"]
["In Thousands, unless otherwise specified","Dec. 31, 2014","Dec. 31, 2013","Dec. 31, 2012"]
["Operating activities"]
["Net loss",-36375,-26088,-11742]
["Adjustments to reconcile net loss to net cash used in operating activities:"]
["Depreciation expense",160,71,139]
["Amortization of debt discount and beneficial conversion",15,459,117]
["Amortization of debt issuance costs",16,19,15]
["Amortization of premiums and discounts on investments",202,47]
["Revaluation of warrants",null,2587,-32]
["Noncash interest expense on convertible notes",null,459,1370]
["Stock-based compensation expense",3679,1227,80]
["Loss related to assets held for sale",29,27,87]
["Loss/(Gain) on sale of assets",2,-148,-3]
["Changes in assets and liabilities:"]
["Prepaids and other assets",-332,27,-429]
["Accounts payable",-299,1756,-215]
["Other accrued liabilities",882,1443,-195]
["Net cash used in operating activities",-32021,-18114,-10808]
["Investing activities"]
["Purchases of investments",-48088,-24677]
["Proceeds from sales/maturities of investments",12351,3505]
["Proceeds from sale of assets",12,201,5]
["Purchase of property and equipment",-873,-31,-7]
["Net cash used in investing activities",-36598,-21002,-2]
["Financing activities"]
["Proceeds from issuance of common stock, net of issuance costs",91731,72194]
["Proceeds from issuance of preferred stock, net of issuance costs",null,16824]
["Proceeds from exercise of common stock options",473,123,41]
["Proceeds from warrant issuance",78,null,298]
["Proceeds from debt issuance, net of issuance costs",4838,null,15412]
["Net cash provided by financing activities",97120,89141,15751]
["Net increase in cash and cash equivalents",28501,50025,4941]
["Cash and cash equivalents at beginning of period",56537,6512,1571]
["Cash and cash equivalents at end of period",85038,56537,6512]
["Supplemental disclosure of cash flow information:"]
["Deferred offering costs not yet paid",107]
["10% Convertible promissory notes"]
["Supplemental disclosure of cash flow information:"]
["Conversion of promissory notes, including accrued interest into Series A - 1 preferred stock",null,16623]
["Pfizer note"]
["Supplemental disclosure of cash flow information:"]
["Conversion of promissory notes, including accrued interest into Series A - 1 preferred stock",null,7803]

{"sheet":"Condensed_Statements_of_Cash_F1","index":7,"n_rows":6,"n_cols":2,"rows_kept":6,"cut":false,"hidden":false,"merged":[[0,1,1,1]]}
["Condensed Statements of Cash Flows (Parenthetical) (USD $)","Dec. 31, 2014"]
["In Thousands, unless otherwise specified"]
["10% Convertible promissory notes"]
["Conversion of convertible promissory notes into preferred stock, accrued interest",923]
["Pfizer note"]
["Conversion of convertible promissory notes into preferred stock, accrued interest",274]

{"sheet":"The_Company_and_Basis_of_Prese","index":8,"n_rows":23,"n_cols":6,"rows_kept":23,"cut":false,"hidden":false,"merged":[[24,1,24,5],[8,1,8,5],[9,1,9,5],[10,1,10,5],[11,1,11,5],[12,1,12,5],[23,1,23,5],[0,0,1,0],[0,1,0,5],[1,1,1,5],[2,1,2,5],[3,0,24,0],[3,1,3,5],[4,1,4,5],[5,1,5,5],[6,1,6,5],[7,1,7,5]]}
["The Company and Basis of Presentation","12 Months Ended"]
[null,"Dec. 31, 2014"]
["The Company and Basis of Presentation"]
["The Company and Basis of Presentation","1. The Company and Basis of Presentation "]
[null,"        The Company is an emerging pharmaceutical company whose planned principal operations are focused on developing and commercializing first-in-class, oral, low-density lipoprotein cholesterol (“LDL-cholesterol”) lowering therapies for the treatment of hypercholesterolemia and other cardiometabolic risk markers. ETC-1002, the Company's lead product candidate, is a first-in-class, orally available, once-daily small molecule designed to lower LDL-cholesterol levels and avoid many of the side effects associated with other LDL-cholesterol lowering therapies currently available. ETC-1002 is being developed for patients with hypercholesterolemia. One completed Phase 2b clinical study and a second that is nearing completion build upon a successful and comprehensive Phase 1 and Phase 2 clinical development program for ETC-1002. The Company owns the exclusive worldwide rights to ETC-1002. "]
[null,"        The Company's primary activities since incorporation have been conducting research and development activities, including nonclinical, preclinical and clinical testing, performing business and financial planning, recruiting personnel, and raising capital. Accordingly, the Company has not commenced principal operations and is subject to risks and uncertainties which include the need to research, develop, and clinically test potential therapeutic products; obtain regulatory approvals for its products and commercialize them, if approved; expand its management and scientific staff; and finance its operations with an ultimate goal of achieving profitable operations. "]
[null,"        The Company has sustained operating losses since inception and expects such losses to continue over the foreseeable future. Management plans to continue to fund operations through public or private equity or debt financings or through other sources, which may include collaborations with third parties. If adequate funds are not available, the Company may not be able to continue the development of its current or future product candidates, or to commercialize its current or future product candidates, if approved. "]
[null,"Reverse Stock Split "]
[null,"        On June 11, 2013, in connection with its initial public offering (the “IPO”), the Company effectuated a 1-for-6.986 reverse stock split of its outstanding common stock, which was approved by the Company's board of directors on June 5, 2013. The reverse stock split resulted in an adjustment to the Series A preferred stock and Series A-1 preferred stock conversion prices to reflect a proportional decrease in the number of shares of common stock to be issued upon conversion. The accompanying financial statements and notes to the financial statements give effect to the reverse stock split for all periods presented. The shares of common stock retained a par value of $0.001 per share. Accordingly, the stockholders' equity reflects the reverse stock split by reclassifying from \"common stock\" to \"Additional paid-in capital\" in an amount equal to the par value of the decreased shares resulting from the reverse stock split. "]
[null,"Initial Public Offering "]
[null,"        On July 1, 2013, the Company completed its IPO whereby the Company sold 5,000,000 shares of common stock at a price of $14.00 per share. The shares began trading on the Nasdaq Global Market on June 26, 2013. On July 11, 2013, the underwriters exercised their over-allotment option in full and purchased an additional 750,000 shares of common stock at a price of $14.00 per share. The Company received approximately $72.2 million in net proceeds from the IPO, including proceeds from the exercise of the underwriters' over-allotment option, net of underwriting discounts and commissions and offering expenses. Upon closing of the IPO, all outstanding shares of preferred stock converted into 9,210,999 shares of common stock; and warrants exercisable for convertible preferred stock were automatically converted into warrants exercisable for 277,690 shares of common stock, resulting in the reclassification of the related convertible preferred stock warrant liability of $2.9 million to additional paid-in capital (See Note 4). "]
[null,"        The following table summarizes the Company's capitalization upon closing of its initial public offering: "]
[null,"                                                                                                                                                                                    "]
[null,"Total common stock issued as of June 30, 2013",null,null,"396,414 "]
[null,"Conversion of Series A preferred stock into common stock upon closing of IPO",null,null,"8,244,781 "]
[null,"Conversion of Series A-1 preferred stock into common stock upon closing of IPO",null,null,"966,218 "]
[null,"Sales of common stock through IPO",null,null,"5,000,000 "]
[null,"​","​","​  ","​  ","​"]
[null,"Common stock issued as of July 1, 2013",null,null,"14,607,413 "]
[null,"Issuance of common stock to underwriters due to exercise of over-allotment",null,null,"750,000 "]
[null,"​","​","​  ","​  ","​"]
[null,"Total common stock issued as of July 11, 2013",null,null,"15,357,413 "]
[null,"​","​","​  ","​  ","​"]

{"sheet":"Summary_of_Significant_Account","index":9,"n_rows":36,"n_cols":2,"rows_kept":36,"cut":false,"hidden":false,"merged":[[0,0,1,0],[3,0,36,0]]}
["Summary of Significant Accounting Policies","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Summary of Significant Accounting Policies"]
["Summary of Significant Accounting Policies","2. Summary of Significant Accounting Policies "]
[null,"Use of Estimates "]
[null,"        The preparation of financial statements in conformity with U.S. generally accepted accounting principles (“GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, expenses and related disclosures. Actual results could differ from those estimates. "]
[null,"        Prior to the completion of the IPO on July 1, 2013, the Company utilized significant estimates and assumptions in determining the fair value of its common stock. The Company utilized valuation methodologies in accordance with the framework of the 2004 American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its common stock. Each valuation methodology includes estimates and assumptions that require the Company's judgment. These estimates and assumptions include a number of objective and subjective factors, including external market conditions affecting the biotechnology industry sector, the prices at which the Company sold shares of its preferred stock, the superior rights and preferences of securities senior to its common stock at the time and the likelihood of achieving a liquidity event, such as an initial public offering or sale. Significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date. "]
[null,"Cash and Cash Equivalents "]
[null,"        The Company invests its excess cash in bank deposits, money market accounts, and short-term investments. The Company considers all highly liquid investments with an original maturity of 90 days or less at the time of purchase to be cash equivalents. Cash equivalents are reported at fair value. "]
[null,"Investments "]
[null,"        Investments are considered to be available-for-sale and are carried at fair value. Unrealized gains and losses, if any, are reported as a separate component of stockholders' equity. The cost of investments classified as available-for-sale are adjusted for the amortization of premiums and accretion of discounts to maturity and recorded in other income (expense), net. Realized gains and losses, if any, are determined using the specific identification method and recorded in other income (expense), net. Investments with original maturities beyond 90 days at the date of purchase and which mature at, or less than twelve months from, the balance sheet date are classified as current. Investments with a maturity beyond twelve months from the balance sheet date are classified as long-term. "]
[null,"Concentration of Credit Risk "]
[null,"        Cash, cash equivalents, and marketable securities consist of financial instruments that potentially subject the Company to concentrations of credit risk. The Company has established guidelines for investment of its excess cash and believes the guidelines maintain safety and liquidity through diversification of counterparties and maturities. "]
[null,"Segment Information "]
[null,"        The Company views its operations and manages its business in one operating segment, which is the business of researching, developing and commercializing therapies for the treatment of patients with elevated levels of LDL-cholesterol and other cardiometabolic risk markers. "]
[null,"Fair Value of Financial Instruments "]
[null,"        The Company's cash, cash equivalents and investments are carried at fair value. Financial instruments, including other prepaid and current assets, accounts payable and accrued liabilities are carried at cost, which approximates fair value. Debt is carried at amortized cost, which approximates fair value. "]
[null,"Property and Equipment, Net "]
[null,"        Property and equipment are recorded at cost, less accumulated depreciation. Depreciation is provided using the straight-line method over the estimated useful lives of the respective assets, generally three to ten years. Leasehold improvements are amortized over the lesser of the lease term or the estimated useful lives of the related assets. "]
[null,"Impairment of Long-Lived Assets "]
[null,"        The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. The impairment loss, if recognized, would be based on the excess of the carrying value of the impaired asset over its respective fair value. Excluding impairment losses recorded on assets held for sale, no other impairment losses have been recorded through December 31, 2014. "]
[null,"Research and Development "]
[null,"        Research and development expenses consist of costs incurred to further the Company's research and development activities and include salaries and related benefits, costs associated with study studies, nonclinical activities (such as toxicology studies), regulatory activities, manufacturing activities to support clinical activities, research-related overhead expenses, and fees paid to external service providers that conduct certain research and development, clinical, and manufacturing activities on behalf of the Company. Research and development costs are expensed as incurred. "]
[null,"In-Process Research and Development "]
[null,"        In April 2008, the Company acquired certain tangible research and development assets and intellectual property from Pfizer Inc. (“Pfizer”). As the acquired in-process research and development had not reached technological feasibility and had no alternative future uses in connection with this asset and intellectual property acquisition and the related purchase price allocation, the Company expensed $0.1 million as in-process research and development costs in 2008. "]
[null,"Accrued Clinical Development Costs "]
[null,"        Outside research costs are a component of research and development expense. These expenses include fees paid to contract research organizations and other service providers that conduct certain clinical and product development activities on behalf of the Company. Depending upon the timing of payments to the service providers, the Company recognizes prepaid expenses or accrued expenses related to these costs. These accrued or prepaid expenses are based on management's estimates of the work performed under service agreements, milestones achieved and experience with similar contracts. The Company monitors each of these factors and adjusts estimates accordingly. "]
[null,"Income Taxes "]
[null,"        The Company utilizes the liability method of accounting for income taxes as required by ASC 740, Income Taxes. Under this method, deferred tax assets and liabilities are determined based on differences between financial reporting and the tax basis of assets and liabilities and are measured using enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company has incurred operating losses since inception. Accordingly, it is not more likely than not that the Company will realize deferred tax assets and as such, it has recorded a full valuation allowance. "]
[null,"Warrants "]
[null,"        The Company accounts for its warrants issued in connection with its various financing transactions based upon the characteristics and provisions of the instrument. Warrants classified as liabilities are recorded on the Company's balance sheet at their fair value on the date of issuance and are marked-to-market on each subsequent reporting period, with the fair value changes recognized in the statement of operations. Warrants classified as additional-paid-in-capital are recorded on the Company's balance sheet at their fair value on the date of issuance. The warrants are measured using the Black-Scholes option-pricing model subsequent to the pricing of the Company's IPO and a Monte Carlo valuation model for previous periods which are based, in part, upon inputs where there is little or no market data, requiring the Company to develop its own independent assumptions. (See Note 4). "]
[null,"Stock-Based Compensation "]
[null,"        The Company accounts for stock-based compensation in accordance with the provisions of ASC 718, Compensation—Stock Compensation. Accordingly, compensation costs related to equity instruments granted are recognized over the requisite service periods of the awards on a straight-line basis at the grant-date fair value calculated using a Black-Scholes option pricing model. Additionally, under the provisions of ASC 718, the Company is required to include an estimate of the number of awards that will be forfeited in calculating compensation costs. Any changes to the estimated forfeiture rates are accounted for prospectively. Stock-based compensation arrangements with non-employees are recognized at the grant-date fair value and then re-measured at each reporting period. Expense is recognized during the period the related services are rendered. "]
[null,"Recent Accounting Pronouncements "]
[null,"        In June 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-10 which improves financial reporting by reducing the cost and complexity associated with the incremental reporting requirements for development stage entities without reducing the relevance of information provided to users of financial statements. Under the amended guidance, issuers are no longer required to (1) present inception-to-date information in the statements of income, cash flows, and shareholder equity, (2) label the financial statements as those of a development stage entity, (3) disclose a description of the development stage activities in which the entity is engaged, and (4) disclose in the first year in which the entity is no longer a development stage entity that in prior years it had been in the development stage. The Company adopted the amendment which resulted in a reduction in disclosures previously relating to a development stage entity. "]
[null,"        In August 2014, the FASB issued ASU 2014-15 which requires management of public companies to evaluate whether there are conditions and events that raise substantial doubt about the entity's ability to continue as a going concern within one year after the financial statements are issued and, if so, to disclose that fact. Management will be required to make this evaluation for both annual and interim reporting periods, if applicable. Management is also required to evaluate and disclose whether its plans alleviate that doubt. The standard is effective for annual periods ending after December 15, 2016 and interim periods within annual periods beginning after December 15, 2016. Early adoption is permitted for annual or interim reporting periods for which the financial statements have not previously been issued. The Company does not believe the adoption of this standard will have a material impact on its financial position, results of operations or related financial statement disclosures."]

{"sheet":"Debt","index":10,"n_rows":27,"n_cols":6,"rows_kept":27,"cut":false,"hidden":false,"merged":[[23,1,23,5],[24,1,24,5],[25,1,25,5],[26,1,26,5],[27,1,27,5],[7,1,7,5],[8,1,8,5],[9,1,9,5],[10,1,10,5],[21,1,21,5],[22,1,22,5],[11,3,11,4],[0,0,1,0],[0,1,0,5],[1,1,1,5],[2,1,2,5],[3,0,27,0],[3,1,3,5],[4,1,4,5],[5,1,5,5],[6,1,6,5]]}
["Debt","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Debt"]
["Debt","3. Debt "]
[null,"Credit Facility "]
[null,"        In June 2014, the Company entered into a loan and security agreement (the \"Credit Facility\") with Oxford Finance LLC which provides for initial borrowings of $5.0 million under term loans (\"Term A Loan\") and additional borrowings of $15.0 million (\"Term B Loan\") at the Company's option, for a maximum of $20.0 million. On June 30, 2014, the Company received proceeds of $5.0 million from the issuance of secured promissory notes under the Term A Loan. The remaining $15.0 million available under Term B Loan becomes available to be drawn down, at the Company's sole discretion, until March 31, 2015, upon achieving positive development results in the Company's ongoing Phase 2b clinical study (a \"Milestone Event\"). All secured promissory notes issued under the Credit Facility are due on July 1, 2018 and are collateralized by substantially all of the Company's personal property, other than its intellectual property. "]
[null,"        The Company is obligated to make monthly, interest-only payments on Term A Loan until July 1, 2015 and, thereafter, to pay 36 consecutive equal monthly installments of principal and interest from August 1, 2015 through July 1, 2018. If a Milestone Event is achieved and the Company elects to make additional borrowings under the Term B Loan, the term of monthly, interest-only payments will be extended until January 1, 2016. Term A Loan bears interest at an annual rate of 6.40%. In the event the Company enters into Term B Loan, the interest rate will be the greater of (i) 6.40% or (ii) three month LIBOR rate three business days prior to the funding of the new term loan plus an additional 6.17%. In addition, a final payment equal to 8.0% of any amounts drawn under the Credit Facility is due upon the earlier of the maturity date or prepayment of the term loans. The Company is recognizing the final payment as interest expense using the effective interest method over the life of the Credit Facility. "]
[null,"        There are no financial covenants associated to the Credit Facility. However, so long as the Credit Facility is outstanding, there are negative covenants that limit or restrict the Company's activities, which include limitations on incurring indebtedness, granting liens, mergers or acquisitions, dispositions of assets, making certain investments, entering into certain transactions with affiliates, paying dividends or distributions, encumbering or pledging interest in its intellectual property and certain other business transactions. Additionally, the Credit Facility also includes events of default, the occurrence and continuation of any of which provides the lenders the right to exercise remedies against the Company and the collateral securing the loans under the Credit Facility, which includes cash. These events of default include, among other things, non-payment of any amounts due under the Credit Facility, insolvency, the occurrence of a material adverse event, inaccuracy of representations and warranties, cross default to material indebtedness and a material judgment against the Company. Upon the occurrence of an event of default, all obligations under the Credit Facility shall accrue interest at a rate equal to the fixed annual rate plus five percentage points. "]
[null,"        In connection with the borrowing of Term A Loan, the Company issued a warrant (the \"Warrant\") to purchase 8,230 shares of common stock at an exercise price of $15.19 (see Note 4). The Warrant resulted in a debt discount of $0.1 million which is amortized into interest expense using the effective interest method over the life of Term A Loan. In addition, deferred financing costs of $0.1 million included in other prepaid and current assets on the consolidated balance sheet as of December 31, 2014 are amortized to interest expense using the effective-interest method over the same term. As of December 31, 2014, the remaining unamortized discount and debt issuance costs associated with the debt were $0.1 million and $0.1 million, respectively. "]
[null,"        Estimated future principal payments due under the Credit Facility are as follows: "]
[null,"                                                                                                                                                                                    "]
[null,"Years Ending December 31, ",null,"(in thousands) "]
[null,2014,null,"$","—"]
[null,2015,null,null,"638 "]
[null,2016,null,null,"1,604 "]
[null,2017,null,null,"1,709 "]
[null,2018,null,null,"1,049 "]
[null,"​","​","​  ","​  ","​"]
[null,"Total",null,"$","5,000 "]
[null,"​","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​  "]
[null,"        During the year ended December 31, 2014, the Company recognized $0.3 million of interest expense and made cash interest payments of $0.1 million related to the Credit Facility. "]
[null,"Convertible Notes "]
[null,"        In January 2012, the Company issued $6.0 million of 10% convertible promissory notes to certain existing investors for cash. In September and November 2012, the Company issued the aggregate of $9.7 million of 10% convertible promissory notes that mature on September 4, 2013 for cash to certain existing investors. In connection with the September convertible note financing, the Company and the holders of the January 2012 convertible promissory notes agreed to extend the maturity date of the January 2012 notes to September 4, 2013. In February 2013, these convertible promissory notes, with an outstanding principal of $15.7 million and accrued interest of $0.9 million, were amended and then converted into 16,623,092 shares of Series A preferred stock, in accordance with their terms and at their conversion price of $1.00 per share, and following such conversion, the notes were cancelled. "]
[null,"        The holders of the September convertible promissory notes received the benefit of a deemed conversion price of the September convertible promissory notes that were below the estimated fair value of the Series A convertible preferred stock at the time of their issuance. The fair value of this beneficial conversion feature was estimated to be $0.3 million. The fair value of this beneficial conversion feature was recorded to debt discount and amortized to interest expense using the effective interest method over the term of the convertible promissory notes. As a result of the conversion of the convertible promissory notes into shares of Series A preferred stock in February 2013, the Company recorded the remaining accretion of the beneficial conversion feature of $0.2 million as interest expense during the year ended December 31, 2013. "]
[null,"        In connection with the issuance of the September and the November 2012 convertible promissory notes, the Company issued warrants to purchase shares of Series A preferred stock for an aggregate price of $9,700. The estimated fair value of the warrants at issuance was $0.3 million. The proceeds from the sale of the preferred stock and warrants were allocated with $9.4 million to the convertible promissory notes and $0.3 million to warrants. This resulted in a discount on the convertible promissory notes which was amortized into interest expense, using the effective interest method, over the life of the convertible promissory notes (see Note 4). The company recorded $0.1 million of interest expense for the accretion of the discount during the year ended December 31, 2012. As a result of the conversion of the convertible promissory notes into shares of Series A preferred stock in February 2013, the Company recorded $0.2 million of interest expense for the accretion of this discount during the year ended December 31 2013. "]
[null,"        In April 2008, the Company acquired all of the capital stock of Esperion from Pfizer in exchange for a non-subordinated convertible note in the original principal amount of $5.0 million. This convertible promissory note had a maturity date of April 28, 2018. The note bore interest at 8.931% annually, payable semiannually on June 30 and December 31 by adding such unpaid interest to the principal of the note, which would thereafter accrue interest. The Company accrued interest of $0.3 million and $0.6 million during the years ended December 31, 2013 and 2012, respectively. In May 2013 the Company entered into a stock purchase agreement with Pfizer Inc. and sold 6,750,000 shares of Series A-1 preferred stock at a price of $1.1560 per share, which was the fair value at the transaction date. The purchase price was paid through the cancellation of all outstanding indebtedness, including accrued interest, under the Pfizer convertible promissory note, which had an outstanding balance, including accrued interest, of $7.8 million as of May 29, 2013. The Series A-1 preferred stock issued in connection with this transaction was subsequently converted into 966,218 shares of common stock upon completion of the IPO on July 1, 2013. "]

{"sheet":"Warrants","index":11,"n_rows":9,"n_cols":2,"rows_kept":9,"cut":false,"hidden":false,"merged":[[0,0,1,0],[3,0,9,0]]}
["Warrants","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Warrants"]
["Warrants","4. Warrants "]
[null,"        In connection with the Credit Facility entered into in June 2014, the Company issued a warrant to purchase 8,230 shares of common stock at an exercise price of $15.19. The warrant will terminate on the earlier of June 30, 2019 and the closing of a merger or consolidation transaction in which the Company is not the surviving entity. The warrant was recorded at fair value of $0.1 million to additional-paid-in-capital in accordance with ASC 815-10 based upon the allocation of the debt proceeds. The Company estimated the fair value of the warrant using a Black-Scholes option-pricing model, which is based, in part, upon subjective assumptions including but not limited to stock price volatility, the expected life of the warrant, the risk-free interest rate and the fair value of the common stock underlying the warrant. The Company estimates the volatility of its stock based on public company peer group historical volatility that is in line with the expected remaining life of the warrant. The risk-free interest rate is based on the U.S. Treasury zero-coupon bond for a maturity similar to the expected remaining life of the warrant. The expected remaining life of the warrant is assumed to be equivalent to its remaining contractual term. "]
[null,"        In connection with its various convertible note financing transactions, the Company issued warrants to purchase shares of preferred stock which had provisions where the underlying issuance was contingently redeemable based on events outside the Company's control and were recorded as a liability in accordance with ASC 480-10. The warrants were classified as liabilities and were recorded on the Company's balance sheet at fair value on the date of issuance and marked-to-market on each subsequent reporting period, with the fair value changes recognized in the statement of operations. Subsequent to the pricing of the IPO, the Company estimated the fair values of the warrants at each reporting period using a Black-Scholes option-pricing model, which is based, in part, upon subjective assumptions including but not limited to stock price volatility, the expected life of the warrants, the risk-free interest rate and the fair value of the common stock underlying the warrants. The Company estimates the volatility of its stock based on public company peer group historical volatility that is in line with the expected remaining life of the warrants. The risk-free interest rate is based on the U.S. Treasury zero-coupon bond for a maturity similar to the expected remaining life of the warrants. The expected remaining life of the warrants is assumed to be equivalent to their remaining contractual term. Prior to the pricing of the IPO, a Monte Carlo valuation model was utilized to estimate the fair value of the warrants based on the probability and timing of future financings. "]
[null,"        The assumptions used in calculating the estimated fair market value at each reporting period prior to the closing of the Company's IPO represented the Company's best estimate, however, do involve inherent uncertainties. The estimated fair value of the warrants was determined using the Monte Carlo valuation model which totaled $0.3 million and was comprised of $0.1 million and $0.2 million as of and for the September and November 2012 financing, respectively, and was recorded as a discount on the related convertible promissory notes and amortized as interest expense over the term of the convertible promissory notes. Inherent in the Monte Carlo valuation model are assumptions related to expected stock-price volatility, expected life and risk-free interest rate. The Company estimates the volatility of its stock based on public company peer group historical volatility that is in line with the expected remaining life of the warrants. The risk-free interest rate is based on the U.S. Treasury zero-coupon bond on the grant date for a maturity similar to the expected remaining life of the warrants. The expected life of the warrants is assumed to be equivalent to their remaining contractual term. The dividend rate is based on the historical rate, which the Company anticipates to remain at zero. The Monte Carlo model was used prior to the closing of the Company's IPO to appropriately value the potential future exercise price based on various exit scenarios. This requires Level 3 inputs which are based on the Company's estimates of the probability and timing of potential future financings. "]
[null,"        Upon the closing of the Company's IPO, all warrants exercisable for 1,940,000 shares of Series A preferred stock, at an exercise price of $1.00 per share (unadjusted for stock splits), were automatically converted into warrants exercisable for 277,690 shares of common stock, at an exercise price of $6.99 per share. As a result, the Company concluded the warrants outstanding no longer met the criteria to be classified as liabilities and were reclassified to additional paid-in capital at fair value on the date of reclassification. The 277,690 warrants outstanding as of December 31, 2014 expire in February 2018. During the years ended December 31, 2014, 2013 and 2012, the Company recognized a gain/(loss) of $0, $(2.6 million) and less than $0.1 million, respectively, relating to the change in the fair value of the warrant liability. "]
[null,"        As of December 31, 2014, the Company had warrants outstanding that were exercisable for a total of 285,920 shares of common stock at a weighted-average exercise price of $7.23 per share. "]

{"sheet":"Commitments_and_contingencies","index":12,"n_rows":17,"n_cols":18,"rows_kept":17,"cut":false,"hidden":false,"merged":[[6,1,6,17],[7,1,7,17],[16,1,16,17],[17,1,17,17],[8,17,9,17],[10,3,10,16],[0,0,1,0],[0,1,0,17],[1,1,1,17],[2,1,2,17],[3,0,17,0],[3,1,3,17],[4,1,4,17],[5,1,5,17],[8,8,9,8],[8,9,9,10],[8,11,9,11],[8,12,9,13],[8,14,9,14],[8,15,8,16],[9,15,9,16],[8,1,9,1],[8,2,9,2],[8,3,9,4],[8,5,9,5],[8,6,8,7],[9,6,9,7]]}
["Commitments and contingencies","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Commitments and contingencies"]
["Commitments and contingencies","5. Commitments and contingencies "]
[null,"        In February 2014, the Company entered into an operating lease agreement for its principal executive offices located in Ann Arbor, Michigan commencing in April 2014 with a term of 63 months. The Company's lease provides for fixed monthly rent for the term of the lease, with monthly rent increasing every 12 months subsequent to the first three months of the lease, and also provides for certain rent adjustments to be paid as determined by the landlord. "]
[null,"        In May 2014, the Company entered into the third amendment to the operating lease agreement for its laboratory facility in Plymouth, Michigan. The amendment provides in part that (i) the expiration date of the term of the lease is extended from April 2014 to April 2017, (ii) the rentable laboratory space is adjusted to 3,045 square feet, (iii) the Company's proportionate share of the landlord's expenses and taxes is adjusted to 7.40%, (iv) the Company may exercise its option to renew the lease for one term of three years through written notice to the landlord by February 2017 and (v) the annual base rent under the lease is decreased to $37,000, subject to increase and adjustments provided in the lease. "]
[null,"        The total rent expense for the years ended December 31, 2014, 2013 and 2012 was approximately $0.3 million, $0.3 million and $0.3 million, respectively. The following table summarizes the Company's future minimum lease payments as of December 31, 2014: "]
[null,"                                                                                                                                                                                    "]
[null,null,null,"Total ",null,null,"Less than",null,null,"1 - 3 Years ",null,null,"3 - 5 Years ",null,null,"More than"]
[{"$nulls":6},"1 Year ",{"$nulls":8},"5 Years "]
[null,null,null,"(in thousands)"]
[null,"Operating lease",null,"$","552 ",null,"$","133 ",null,"$","251 ",null,"$","168 ",null,"$","—  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total",null,"$","552 ",null,"$","133 ",null,"$","251 ",null,"$","168 ",null,"$","—  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​  "]
[null,"        The Company also holds a license agreement in which it is obligated to make future minimum annual payments of $50,000 in years where there is not a milestone payment required under the terms of the agreement (see Note 14). Further, the Company is contractually obligated to issue up to an aggregate of 11,451 shares of common stock upon meeting various future milestones set forth in the agreement. "]

{"sheet":"Property_and_Equipment","index":13,"n_rows":23,"n_cols":9,"rows_kept":23,"cut":false,"hidden":false,"merged":[[4,1,4,8],[5,1,5,8],[22,1,22,8],[23,1,23,8],[6,3,6,7],[7,3,7,4],[7,6,7,7],[8,3,8,7],[0,0,1,0],[0,1,0,8],[1,1,1,8],[2,1,2,8],[3,0,23,0],[3,1,3,8]]}
["Property and Equipment","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Property and Equipment"]
["Property and Equipment","6. Property and Equipment "]
[null,"        Property and equipment consist of the following: "]
[null,"                                                                                                                                                                                    "]
[null,null,null,"December 31, "]
[null,null,null,2014,null,null,2013]
[null,null,null,"(in thousands)"]
[null,"Lab equipment",null,"$","519 ",null,"$","511 "]
[null,"Computer equipment",null,null,"110 ",null,null,"100 "]
[null,"Software",null,null,"74 ",null,null,"119 "]
[null,"Furniture and fixtures",null,null,"320 ",null,null,"11 "]
[null,"Leasehold improvements",null,null,"158 ",null,null,"21 "]
[null,"Assets in Progress",null,null,"2 ",null,null,"7 "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Subtotal",null,null,"1,183 ",null,null,"769 "]
[null,"Less accumulated depreciation and amortization",null,null,"403 ",null,null,"688 "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Property and equipment, net",null,"$","780 ",null,"$","81 "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​  "]
[null,"        Depreciation expense was $0.2 million, $0.1 million, and $0.1 million for the years ended December 31, 2014, 2013 and 2012, respectively. "]

{"sheet":"Other_Accrued_Liabilities","index":14,"n_rows":18,"n_cols":9,"rows_kept":18,"cut":false,"hidden":false,"merged":[[4,1,4,8],[5,1,5,8],[18,1,18,8],[19,1,19,8],[6,3,6,7],[7,3,7,4],[7,6,7,7],[8,3,8,7],[0,0,1,0],[0,1,0,8],[1,1,1,8],[2,1,2,8],[3,0,19,0],[3,1,3,8]]}
["Other Accrued Liabilities","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Other Accrued Liabilities"]
["Other Accrued Liabilities","7. Other Accrued Liabilities "]
[null,"        Other accrued liabilities consist of the following: "]
[null,"                                                                                                                                                                                    "]
[null,null,null,"December 31, "]
[null,null,null,2014,null,null,2013]
[null,null,null,"(in thousands)"]
[null,"Accrued compensation",null,"$","313 ",null,"$","667 "]
[null,"Accrued professional fees",null,null,"167 ",null,null,"210 "]
[null,"Accrued franchise and property taxes",null,null,"107 ",null,null,"95 "]
[null,"Accrued interest",null,null,"104 ",null,null,"—"]
[null,"Accrued other",null,null,"144 ",null,null,"115 "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total other accrued liabilities",null,"$","835 ",null,"$","1,087 "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​  "]

{"sheet":"Investments","index":15,"n_rows":48,"n_cols":15,"rows_kept":48,"cut":false,"hidden":false,"merged":[[47,1,47,14],[48,1,48,14],[0,0,1,0],[0,1,0,14],[1,1,1,14],[2,1,2,14],[3,0,48,0],[3,1,3,14],[4,1,4,14],[44,1,44,14],[45,1,45,14],[46,1,46,14],[26,11,28,11],[26,12,26,13],[27,12,27,13],[28,12,28,13],[26,14,28,14],[29,3,29,13],[27,6,27,7],[28,6,28,7],[26,8,28,8],[26,9,26,10],[27,9,27,10],[28,9,28,10],[6,14,8,14],[9,3,9,13],[25,3,25,13],[26,1,28,1],[26,2,28,2],[26,3,26,4],[27,3,27,4],[28,3,28,4],[26,5,28,5],[26,6,26,7],[6,8,8,8],[6,9,6,10],[7,9,7,10],[8,9,8,10],[6,11,8,11],[6,12,6,13],[7,12,7,13],[8,12,8,13],[5,3,5,13],[6,1,8,1],[6,2,8,2],[6,3,6,4],[7,3,7,4],[8,3,8,4],[6,5,8,5],[6,6,6,7],[7,6,7,7],[8,6,8,7]]}
["Investments","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Investments"]
["Investments","8. Investments "]
[null,"        The following table summarizes the Company's cash equivalents and investments: "]
[null,null,null,"December 31, 2014 "]
[null,null,null,"Amortized",null,null,"Gross",null,null,"Gross",null,null,"Estimated"]
[null,null,null,"Cost ",null,null,"Unrealized",null,null,"Unrealized",null,null,"Fair"]
[{"$nulls":6},"Gains ",null,null,"Losses ",null,null,"Value "]
[null,null,null,"(in thousands)"]
[null,"Cash equivalents:"]
[null,"Money market funds",null,"$",357,null,"$","—",null,"$","—",null,"$",357]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Short-term investments:"]
[null,"Certificates of deposit",null,null,2934,null,null,"—",null,null,"—",null,null,2934]
[null,"U.S treasury notes",null,null,9020,null,null,4,null,null,"—",null,null,9024]
[null,"U.S. government agency securities",null,null,8853,null,null,"—",null,null,"(8",")",null,8845]
[null,"Long-term investments:"]
[null,"Certificates of deposit",null,null,1848,null,null,"—",null,null,"—",null,null,1848]
[null,"U.S. treasury notes",null,null,2494,null,null,"—",null,null,"(5",")",null,2489]
[null,"U.S. government agency securities",null,null,31454,null,null,"—",null,null,"(50",")",null,31404]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total",null,"$",56960,null,"$",4,null,"$","(63",")","$",56901]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​  "]
[null,null,null,"December 31, 2013 "]
[null,null,null,"Amortized",null,null,"Gross",null,null,"Gross",null,null,"Estimated"]
[null,null,null,"Cost ",null,null,"Unrealized",null,null,"Unrealized",null,null,"Fair"]
[{"$nulls":6},"Gains ",null,null,"Losses ",null,null,"Value "]
[null,null,null,"(in thousands)"]
[null,"Cash equivalents:"]
[null,"Money market funds",null,"$",5356,null,"$","—",null,"$","—",null,"$",5356]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Short-term investments:"]
[null,"U.S treasury notes",null,null,2071,null,null,"—",null,null,"—",null,null,2071]
[null,"U.S. government agency securities",null,null,1454,null,null,"—",null,null,"—",null,null,1454]
[null,"Long-term investments:"]
[null,"Certificates of deposit",null,null,238,null,null,"—",null,null,"—",null,null,238]
[null,"U.S. treasury notes",null,null,9116,null,null,3,null,null,"(2",")",null,9117]
[null,"U.S. government agency securities",null,null,8187,null,null,1,null,null,"(5",")",null,8183]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total",null,"$",26422,null,"$",4,null,"$","(7",")","$",26419]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​  "]
[]
[]
[null,"At December 31, 2014, remaining contractual maturities of available-for-sale investments classified as current on the balance sheet were less than 12 months, and remaining contractual maturities of available-for-sale investments classified as long-term were less than two years. "]
[null,"        There were no unrealized gains or losses on investments reclassified from accumulated other comprehensive income to other income (expense) in the Statement of Operations during the year ended December 31, 2014. "]

{"sheet":"Fair_Value_Measurements","index":16,"n_rows":42,"n_cols":15,"rows_kept":42,"cut":false,"hidden":false,"merged":[[38,1,38,14],[39,1,39,14],[40,1,40,14],[41,1,41,14],[42,1,42,14],[15,3,15,13],[0,0,1,0],[0,1,0,14],[1,1,1,14],[2,1,2,14],[3,0,42,0],[3,1,3,14],[4,1,4,14],[5,1,5,14],[11,1,11,14],[7,2,8,2],[9,2,10,2],[14,3,14,4],[14,6,14,7],[14,9,14,10],[14,12,14,13],[12,1,12,14]]}
["Fair Value Measurements","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Fair Value Measurements"]
["Fair Value Measurements","9. Fair Value Measurements "]
[null,"        The Company follows accounting guidance that emphasizes that fair value is a market-based measurement, not an entity-specific measurement. Fair value is defined as \"the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.\" Fair value measurements are defined on a three level hierarchy: "]
[null,"                                                                                                                                                                                    "]
[null,"Level 1 inputs:",null,"Quoted prices for identical assets or liabilities in active markets;"]
[]
[null,"Level 2 inputs:",null,"Observable inputs other than Level 1 prices, such as quoted market prices for similar assets or liabilities or other inputs that are observable or can be corroborated by market data; and"]
[]
[null,"Level 3 inputs:",null,"Unobservable inputs that are supported by little or no market activity and require the reporting entity to develop assumptions that market participants would use when pricing the asset or liability."]
[null,"        The following table presents the Company's financial assets and liabilities that have been measured at fair value on a recurring basis: "]
[null,"                                                                                                                                                                                    "]
[]
[null,"Description ",null,"Total ",null,null,"Level 1 ",null,null,"Level 2 ",null,null,"Level 3 "]
[null,null,null,"(in thousands)"]
[null,"December 31, 2014"]
[null,"Assets:"]
[null,"Money market funds",null,"$","357 ",null,"$","357 ",null,"$","—",null,"$","—"]
[null,"Available-for-sale securities:"]
[null,"Certificates of deposit",null,null,"4,782 ",null,null,"4,782 ",null,null,"—",null,null,"—"]
[null,"U.S. treasury notes",null,null,"11,513 ",null,null,"11,513 ",null,null,"—",null,null,"—"]
[null,"U.S. government agency securities",null,null,"40,249 ",null,null,"—",null,null,"40,249 ",null,null,"—  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total assets at fair value",null,"$","56,901 ",null,"$","16,652 ",null,"$","40,249 ",null,"$","—  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​  "]
[null,"December 31, 2013"]
[null,"Assets:"]
[null,"Money market funds",null,"$","5,356 ",null,"$","5,356 ",null,"$","—",null,"$","—"]
[null,"Available-for-sale securities:"]
[null,"Certificates of deposit",null,null,"238 ",null,null,"238 ",null,null,"—",null,null,"—"]
[null,"U.S. treasury notes",null,null,"11,188 ",null,null,"11,188 ",null,null,"—",null,null,"—"]
[null,"U.S. government agency securities",null,null,"9,637 ",null,null,"—",null,null,"9,637 ",null,null,"—  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total assets at fair value",null,"$","26,419 ",null,"$","16,782 ",null,"$","9,637 ",null,"$","—  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​  "]
[]
[null,"        There were no transfers between Levels 1, 2 or 3 during the year ended December 31, 2014 or December 31, 2013. "]
[null,"Fair Value Measurements on a Nonrecurring Basis "]
[null,"        In addition to items that are measured at fair value on a recurring basis, the Company also measures assets held for sale at the lower of its carrying amount or fair value on a nonrecurring basis. The Company recognized an impairment expense and other losses relating to assets held for sale during the year ended December 31, 2014, 2013, and 2012 of $0, less than $0.1 million, and $0.1 million based on recent market sales data for similar equipment less the related costs to sell and recent purchase offers, which are Level 3 inputs. There are no assets held for sale as of December 31, 2014. "]

{"sheet":"Convertible_Preferred_Stock_an","index":17,"n_rows":8,"n_cols":2,"rows_kept":8,"cut":false,"hidden":false,"merged":[[0,0,1,0],[3,0,8,0]]}
["Convertible Preferred Stock and Stockholders' Equity","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Convertible Preferred Stock and Stockholders' Equity"]
["Convertible Preferred Stock and Stockholders' Equity","10. Convertible Preferred Stock and Stockholders' Equity "]
[null,"        In January 2012 the Company issued $6.0 million of 10% convertible promissory notes to certain existing investors for cash. In September and November 2012, the Company issued an aggregate of $9.7 million of 10% convertible promissory notes to certain existing investors for cash. In February 2013, these convertible promissory notes, with an outstanding principal of $15.7 million and accrued interest of $0.9 million, were amended and then converted into 16,623,092 shares of Series A preferred stock, in accordance with their terms and at their conversion price of $1.00 per share, and following such conversion, the notes were cancelled. Each share of Series A preferred stock issued in the financing was convertible into 0.143 shares of common stock upon the closing of the Company's IPO. "]
[null,"        On April 19, 2013, the Company issued and sold an aggregate of 17,000,000 shares of Series A preferred stock at a price of $1.00 per share for proceeds of $16.9 million, which is net of issuance costs of $0.1 million, to funds affiliated with Longitude Capital and certain existing investors. Each share of Series A preferred stock issued in the financing was convertible into 0.143 shares of common stock upon the closing of the Company's IPO. "]
[null,"        On May 29, 2013, the Company entered into a stock purchase agreement with Pfizer Inc. and issued and sold 6,750,000 shares of Series A-1 preferred stock at a price of $1.1560 per share. The purchase price was paid through the cancellation of all outstanding indebtedness, including accrued interest, under the Pfizer convertible promissory note, which had an aggregate balance, including accrued interest, of $7.8 million as of May 29, 2013. Each share of Series A-1 preferred stock issued in the agreement was convertible into 0.143 shares of common stock upon the closing of the Company's IPO. "]
[null,"        Upon the closing of the Company's IPO on July 1, 2013, all of the outstanding shares of convertible preferred stock were converted into 9,210,999 shares of common stock. As of December 31, 2014, the Company did not have any convertible preferred stock issued or outstanding. "]

{"sheet":"Stock_Compensation","index":18,"n_rows":50,"n_cols":15,"rows_kept":50,"cut":false,"hidden":false,"merged":[[50,1,50,14],[37,1,37,14],[38,1,38,14],[39,1,39,14],[47,1,47,14],[48,1,48,14],[49,1,49,14],[8,1,8,14],[9,1,9,14],[10,1,10,14],[11,1,11,14],[25,1,25,14],[26,1,26,14],[0,0,1,0],[0,1,0,14],[1,1,1,14],[2,1,2,14],[3,0,50,0],[3,1,3,14],[4,1,4,14],[5,1,5,14],[6,1,6,14],[7,1,7,14],[40,1,41,1],[40,2,41,2],[40,3,40,10],[41,3,41,10],[40,11,41,11],[42,3,42,4],[42,6,42,7],[42,9,42,10],[27,12,27,13],[28,12,28,13],[29,12,29,13],[30,12,30,13],[27,14,30,14],[31,3,31,4],[31,6,31,7],[31,9,31,10],[31,12,31,13],[27,8,30,8],[27,9,27,10],[28,9,28,10],[29,9,29,10],[30,9,30,10],[27,11,30,11],[30,3,30,4],[27,5,30,5],[27,6,27,7],[28,6,28,7],[29,6,29,7],[30,6,30,7],[12,14,15,14],[16,3,16,4],[16,6,16,7],[16,9,16,10],[16,12,16,13],[27,1,30,1],[27,2,30,2],[27,3,27,4],[28,3,28,4],[29,3,29,4],[12,9,12,10],[13,9,13,10],[14,9,14,10],[15,9,15,10],[12,11,15,11],[12,12,12,13],[13,12,13,13],[14,12,14,13],[15,12,15,13],[12,5,15,5],[12,6,12,7],[13,6,13,7],[14,6,14,7],[15,6,15,7],[12,8,15,8],[12,1,15,1],[12,2,15,2],[12,3,12,4],[13,3,13,4],[14,3,14,4],[15,3,15,4]]}
["Stock Compensation","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Stock Compensation"]
["Stock Compensation","11. Stock Compensation "]
[null,"2013 Stock Option and Incentive Plan "]
[null,"        On June 7, 2013, the Company's stockholders approved the 2013 Stock Option and Incentive Plan (the \"2013 Plan\"), which became effective on June 25, 2013. The number of shares of stock reserved and available for issuance under the 2013 Plan is the sum of (i) 1,100,000, plus (ii) 54,129 shares originally reserved under the Company's 2008 Incentive Stock Option and Restricted Stock Plan (the \"2008 Plan\") that became available for issuance under the 2013 Plan upon completion of the Company's initial public offering, plus (iii) the shares underlying any awards granted under the 2008 Plan that are forfeited, canceled, held back upon the exercise of an option or settlement of an award to cover the exercise price or tax withholding, reacquired by the Company prior to vesting, satisfied without the issuance of stock or otherwise terminated (other than by exercise). Additionally, on each January 1 the number of shares reserved and available for issuance under the 2013 Plan shall be cumulatively increased by two and a half percent of the number of shares issued and outstanding on the immediately preceding December 31 or such lesser number of shares as determined by the plan administrator. "]
[null,"2008 Stock Option and Restricted Stock Plan "]
[null,"        In April 2008, the Company adopted the 2008 Plan, administered by the Board of Directors or a committee appointed by the Board of Directors. The 2008 Plan provides for the granting of stock options and restricted stock to employees and nonemployees of the Company. Options granted under the 2008 Plan may either be incentive stock options (“ISO”s), restricted stock awards (“RSA”s) or nonqualified stock options (“NQSO”s). Stock options and restricted stock grants may be granted to employees, directors and consultants. "]
[null,"        Stock awards under the 2008 Plan may be granted for up to ten years from the adoption of the 2008 Plan at prices no less than 100 percent of the fair value of the shares on the date of the grant as determined by (i) the closing price of the Company's common stock on any national exchange, (ii) the National Association of Securities Dealers Inc. Automated Quotation System (“NASDAQ”), if so authorized for quotation as a NASDAQ security, or (iii) by reasonable application of a reasonable valuation method. The valuation methods utilized by the Company are consistent with the AICPA Technical Practice Aid. "]
[null,"        Under the 2013 Plan and the 2008 Plan the vesting of options granted or restricted awards given will be determined individually with each option grant. Generally, 25 percent of the granted amount will vest upon the first anniversary of the option grant with the remainder vesting ratably on the first day of each calendar quarter for the following three years. Stock options have a 10 year life and expire if not exercised within that period, or if not exercised within 90 days of cessation of providing service to the Company. "]
[null,"        The following table summarizes the activity relating to the Company's options to purchase common stock for the year ended December 31, 2014: "]
[null,"                                                                                                                                                                                    "]
[null,null,null,"Number of",null,null,"Weighted-Average",null,null,"Weighted-Average",null,null,"Aggregate"]
[null,null,null,"Options ",null,null,"Price",null,null,"Remaining",null,null,"Intrinsic"]
[{"$nulls":6},"Per Share ",null,null,"Contractual",null,null,"Value "]
[{"$nulls":9},"Term (Years) "]
[{"$nulls":12},"(in thousands)"]
[null,"Outstanding at December 31, 2013",null,null,1401101,null,"$",9.59,null,null,8.9499999999999993,null,"$",7755]
[null,"Granted",null,null,561500,null,"$",15.03]
[null,"Forfeited or expired (vested and unvested)",null,null,"(125,052",")","$",12.97]
[null,"Exercised",null,null,"(107,963",")","$",4.38]
[null,"​","​","​  ","​  ","​","​","​","​","​","​","​","​","​","​"]
[null,"Outstanding at December 31, 2014",null,null,1729586,null,"$",11.44,null,null,8.43,null,"$",50155]
[null,"​","​","​  ","​  ","​","​","​","​","​","​","​","​","​","​"]
[null,"​","​","​  ","​  ","​","​","​","​","​","​","​","​","​","​  "]
[null,"        The following table summarizes information about the Company's stock option plan as of December 31, 2014: "]
[null,"                                                                                                                                                                                    "]
[null,null,null,"Number of",null,null,"Weighted-Average",null,null,"Weighted-Average",null,null,"Aggregate"]
[null,null,null,"Options ",null,null,"Price",null,null,"Remaining",null,null,"Intrinsic"]
[{"$nulls":6},"Per Share ",null,null,"Contractual",null,null,"Value "]
[{"$nulls":9},"Term (Years) "]
[{"$nulls":12},"(in thousands)"]
[null,"Vested and expected to vest at December 31, 2014",null,null,"1,671,313 ",null,"$","11.37 ",null,null,"8.41 ",null,"$","48,588 "]
[null,"​","​","​  ","​  ","​","​","​","​","​","​","​","​","​","​"]
[null,"Exercisable at December 31, 2014",null,null,"752,397 ",null,"$","6.61 ",null,null,"7.58 ",null,"$","25,452 "]
[null,"​","​","​  ","​  ","​","​","​","​","​","​","​","​","​","​"]
[null,"​","​","​  ","​  ","​","​","​","​","​","​","​","​","​","​  "]
[null,"        The total intrinsic value of stock options exercised during the years ended December 31, 2014, 2013 and 2012 was $1.4 million, $0.2 million and less than $0.1 million, respectively. "]
[null,"        The following table shows the weighted-average assumptions used to compute the stock-based compensation costs for the stock options granted to employees and non-employees during the period from December 31, 2012 to December 31, 2014, using the Black-Scholes option pricing model: "]
[null,"                                                                                                                                                                                    "]
[null,null,null,"Year ended"]
[null,null,null,"December 31, "]
[null,null,null,2014,null,null,2013,null,null,2012]
[null,"Risk-free interest rate",null,null,"1.81 ","%",null,"1.45 ","%",null,"0.85 ","%"]
[null,"Dividend yield",null,null,"—",null,null,"—",null,null,"—"]
[null,"Weighted-average expected life of options (years)",null,null,"6.32 ",null,null,"6.26 ",null,null,"6.25 "]
[null,"Volatility",null,null,"75 ","%",null,"74 ","%",null,"80 ","%"]
[null,"        The risk-free interest rate assumption was based on the United States Treasury's rates for U.S. Treasury zero-coupon bonds with maturities similar to those of the expected term of the award being valued. The assumed dividend yield was based on the Company's expectation of not paying dividends in the foreseeable future. The weighted-average expected life of the options was calculated using the simplified method as prescribed by the Securities and Exchange Commission (“SEC”) Staff Accounting Bulletin No. 107 (“SAB No. 107”). This decision was based on the lack of relevant historical data due to the Company's limited historical experience. In addition, due to the Company's limited historical data, the estimated volatility also reflects the application of SAB No. 107, incorporating the historical volatility of comparable companies whose share prices are publicly available. "]
[null,"        The weighted-average grant-date fair values of stock options granted during the years ended December 31, 2014, 2013, and 2012 were $10.15, $7.14, and $1.33 respectively. During the years ended December 31, 2014, 2013, and 2012, the Company recognized stock-based compensation expense of $3.7 million, $1.2 million, and $0.1 million, respectively. "]
[null,"        As of December 31, 2014, there was approximately $9.3 million of unrecognized compensation cost related to unvested options, adjusted for forfeitures, which will be recognized over a weighted-average period of approximately 2.9 years. "]

{"sheet":"Employee_Benefit_Plan","index":19,"n_rows":5,"n_cols":2,"rows_kept":5,"cut":false,"hidden":false,"merged":[[0,0,1,0],[3,0,5,0]]}
["Employee Benefit Plan","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Employee Benefit Plan"]
["Employee Benefit Plan","12. Employee Benefit Plan "]
[null,"        During 2008, the Company adopted the Esperion Therapeutics, Inc. 401(k) Plan (the \"401(k) Plan\"), which qualifies as a deferred salary arrangement under Section 401(k) of the Internal Revenue Code. Under the 401(k) Plan, participating employees may defer a portion of their pretax earnings. The Company may, at its sole discretion, contribute for the benefit of eligible employees. There have been no Company contributions to the 401(k) Plan during 2014, 2013, or 2012. "]

{"sheet":"Income_Taxes","index":20,"n_rows":40,"n_cols":12,"rows_kept":40,"cut":false,"hidden":false,"merged":[[39,1,39,11],[40,1,40,11],[7,1,7,11],[8,1,8,11],[20,1,20,11],[21,1,21,11],[22,1,22,11],[23,1,23,11],[27,3,27,7],[0,0,1,0],[0,1,0,11],[1,1,1,11],[2,1,2,11],[3,0,40,0],[3,1,3,11],[4,1,4,11],[5,1,5,11],[6,1,6,11],[9,3,9,10],[10,3,10,4],[10,6,10,7],[10,9,10,10],[25,3,25,7],[26,3,26,4],[26,6,26,7],[24,1,24,11]]}
["Income Taxes","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Income Taxes"]
["Income Taxes","13. Income Taxes "]
[null,"        There was no provision for income taxes for the years ended December 31, 2014, 2013 and 2012 because the Company has incurred operating losses since inception. At December 31, 2014, the Company has concluded that it is not more likely than not that the Company will realize the benefit of its deferred tax assets due to its history of losses. Accordingly, the net deferred tax assets have been fully reserved. "]
[null,"        As of December 31, 2014, 2013 and 2012, the Company had deferred tax assets, before valuation allowance, of approximately $34.2 million, $22.8 million and $14.4 million, respectively. Realization of the deferred assets is dependent upon future taxable income, if any, the amount and timing of which are uncertain. Accordingly, the net deferred tax assets have been fully offset by a valuation allowance. "]
[null,"        As of December 31, 2014, 2013 and 2012, the Company had federal net operating loss carryforwards of approximately $95.1 million, $62.3 million and $40.5 million, respectively. The federal net operating loss will expire at various dates beginning in 2028, if not utilized. As of December 31, 2014, 2013 and 2012, the Company had state net operating loss carryforwards of approximately $16.6 million, $33.1 million and $11.3 million, respectively. The state net operating loss will expire at various dates beginning in 2022, if not utilized. The Company has $0.5 million of NOLs related to excess tax benefits generated upon the settlement of stock awards that increased a current year net operating loss. The Company cannot record the benefit of these losses in the financial statements until the losses are utilized to reduce its income taxes payable at which time it will recognize the tax benefit in equity. "]
[null,"        A reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate is as follows: "]
[null,"                                                                                                                                                                                    "]
[null,null,null,"December 31, "]
[null,null,null,2014,null,null,2013,null,null,2012]
[null,"Federal income tax (benefit) at statutory rate",null,null,"(34.0 ",")%",null,"(34.0 ",")%",null,"(34.0 ",")%"]
[null,"Change in Tax Rate",null,null,"2.1 ","%",null,"—","%",null,"—","%"]
[null,"Permanent items",null,null,"1.0 ","%",null,"4.9 ","%",null,"0.4 ","%"]
[null,"Other",null,null,"0.1 ","%",null,"—","%",null,"(0.2 ",")%"]
[null,"Change in valuation allowance",null,null,"30.8 ","%",null,"29.1 ","%",null,"33.8 ","%  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Effective income tax rate",null,null,"0.0 ","%",null,"0.0 ","%",null,"0.0 ","%  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​  "]
[]
[null,"        If the Company experiences a greater than 50 percentage point aggregate change in ownership of certain significant stockholders over a three-year period, a Section 382 ownership change could be deemed to have occurred. If a section 382 change occurs, the Company's future utilization of the net operating loss carryforwards and credits as of the ownership change will be subject to an annual limitation under Section 382 of the Internal Revenue Code of 1986, as amended, and similar state provisions. Such an annual limitation may result in the expiration of net operating losses before utilization. "]
[null,"        The Company's reserves related to taxes are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is more likely than not to be realized following resolution of any potential contingencies present related to the tax benefit. The Company recognized no material adjustment for unrecognized income tax benefits. Through December 31, 2014, the Company had no unrecognized tax benefits or related interest and penalties accrued. "]
[null,"        Significant components of the Company's deferred tax assets are summarized in the table below: "]
[null,"      "]
[null,null,null,"December 31, "]
[null,null,null,2014,null,null,2013]
[null,null,null,"(in thousands)"]
[null,"Deferred tax assets:"]
[null,"Federal and state operating loss carryforwards",null,"$",33099,null,"$",22485]
[null,"Equity Compensation",null,null,971,null,null,206]
[null,"Temporary differences",null,null,138,null,null,113]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total deferred tax assets",null,null,34208,null,null,22804]
[null,"Valuation allowance",null,null,"(34,208",")",null,"(22,804",")"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Net deferred tax assets",null,"$","—",null,"$","—  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​  "]
[null,"                                                                                                                                                                              "]

{"sheet":"License_Agreement","index":21,"n_rows":7,"n_cols":2,"rows_kept":7,"cut":false,"hidden":false,"merged":[[0,0,1,0],[3,0,7,0]]}
["License Agreement","12 Months Ended"]
[null,"Dec. 31, 2014"]
["License Agreement"]
["License Agreement","14. License Agreement "]
[null,"        In December 2011, the Company entered into a license agreement for certain U.S. and foreign patents and patent applications regarding new high-density lipoprotein therapies to treat cardiovascular disease in exchange for 2,862 shares of common stock, plus an issue fee of $50,000. The license agreement will expire in 2028, which is the date of the last to expire of the licensed patents. The Company recorded the common stock, which was valued at its fair value of $4,400, and the issue fee within general and administrative expenses in the statements of operations. "]
[null,"        The license agreement provides for a minimum annual payment of $50,000 for any years in which a milestone is not achieved, fully creditable against any earned royalties per calendar year. In addition, the Company is also contractually obligated to issue up to an aggregate of 11,451 shares of common stock upon various milestones set forth in the agreement. "]
[null,"        Milestone achievement payments are due within 30 days of the milestone achievement. No milestones have been achieved to date under the license agreement. Additionally, the agreement provides for the Company to reimburse the patent holder for certain patent costs during the term of the agreement. The Company recognized expense associated with this license agreement of $50,000 during each of the years ended December 31, 2014, 2013 and 2012, in general and administrative expenses. "]

{"sheet":"Net_Loss_Per_Common_Share","index":22,"n_rows":16,"n_cols":9,"rows_kept":16,"cut":false,"hidden":false,"merged":[[16,1,16,8],[17,1,17,8],[7,8,8,8],[0,0,1,0],[0,1,0,8],[1,1,1,8],[2,1,2,8],[3,0,17,0],[3,1,3,8],[4,1,4,8],[5,1,5,8],[6,1,6,8],[7,1,8,1],[7,2,8,2],[7,3,7,4],[8,3,8,4],[7,5,8,5],[7,6,7,7],[8,6,8,7]]}
["Net Loss Per Common Share","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Net Loss Per Common Share"]
["Net Loss Per Common Share","15. Net Loss Per Common Share "]
[null,"        Basic net loss per share is calculated by dividing net loss by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is computed by dividing net loss by the weighted-average number of common share equivalents outstanding for the period determined using the treasury-stock method. For purposes of this calculation, convertible preferred stock, convertible debt, warrants for preferred stock and stock options are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. Interest expense for convertible debt that is dilutive is added back to net income in the calculation of diluted net loss per share. "]
[null,"        The shares outstanding at the end of the respective periods presented below, after giving effect for the 1-for-6.986 reverse stock split, were excluded from the calculation of diluted net loss per share due to their anti-dilutive effect: "]
[null,"                                                                                                                                                                                    "]
[null,null,null,"December 31,",null,null,"December 31,"]
[null,null,null,2014,null,null,2013]
[null,"Warrants for common stock",null,null,"285,920 ",null,null,"277,690 "]
[null,"Common shares under option",null,null,"1,729,586 ",null,null,"1,401,101 "]
[null,"Unvested restricted stock",null,null,"9,551 ",null,null,"16,703 "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total potential dilutive shares",null,null,"2,025,057 ",null,null,"1,695,494 "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​  "]

{"sheet":"Selected_Quarterly_Financial_D","index":23,"n_rows":45,"n_cols":15,"rows_kept":45,"cut":false,"hidden":false,"merged":[[46,1,46,14],[3,1,3,14],[4,1,4,14],[5,1,5,14],[25,1,25,14],[26,1,26,14],[45,1,45,14],[27,3,27,13],[28,3,28,4],[28,6,28,7],[28,9,28,10],[28,12,28,13],[0,0,1,0],[0,1,0,14],[1,1,1,14],[2,1,2,14],[3,0,46,0],[6,3,6,13],[7,3,7,4],[7,6,7,7],[7,9,7,10],[7,12,7,13],[8,3,8,13]]}
["Selected Quarterly Financial Data (Unaudited)","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Selected Quarterly Financial Data (Unaudited)"]
["Selected Quarterly Financial Data (Unaudited)","16. Selected Quarterly Financial Data (Unaudited) "]
[null,"        The following table summarizes the unaudited quarterly financial data for the last two years: "]
[null,"                                                                                                                                                                                    "]
[null,null,null,2014]
[null,null,null,"March 31 ",null,null,"June 30 ",null,null,"September 30 ",null,null,"December 31 "]
[null,null,null,"(in thousands, except share and per share data)"]
[null,"Operating expenses:"]
[null,"Research and development",null,"$",5400,null,"$",6528,null,"$",7174,null,"$",6200]
[null,"General and administrative",null,null,2490,null,null,2726,null,null,2526,null,null,3180]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total operating expenses",null,null,7890,null,null,9254,null,null,9700,null,null,9380]
[null,"Loss from operations:",null,null,"(7,890",")",null,"(9,254",")",null,"(9,700",")",null,"(9,380",")"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Interest expense",null,null,"—",null,null,"(1",")",null,"(135",")",null,"(134",")"]
[null,"Change in fair value of warrant liability",null,null,"—",null,null,"—",null,null,"—",null,null,"—"]
[null,"Other income (expense), net",null,null,16,null,null,17,null,null,29,null,null,57]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Net loss",null,"$","(7,874",")","$","(9,238",")","$","(9,806",")","$","(9,457",")"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​  "]
[null,"Net loss per common share (basic and diluted)",null,"$","(0.51",")","$","(0.60",")","$","(0.64",")","$","(0.49",")"]
[null,"Weighted-average shares outstanding (basic and diluted)",null,null,15369055,null,null,15399018,null,null,15432641,null,null,19276639]
[]
[null,"                                                                                                                                                                                    "]
[null,null,null,2013]
[null,null,null,"March 31 ",null,null,"June 30 ",null,null,"September 30 ",null,null,"December 31 "]
[null,"Operating expenses:"]
[null,"Research and development",null,"$",2093,null,"$",3100,null,"$",3483,null,"$",7338]
[null,"General and administrative",null,null,1251,null,null,1172,null,null,1924,null,null,2398]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total operating expenses",null,null,3344,null,null,4272,null,null,5407,null,null,9736]
[null,"Loss from operations:",null,null,"(3,344",")",null,"(4,272",")",null,"(5,407",")",null,"(9,736",")"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Interest expense",null,null,"(828",")",null,"(108",")",null,"—",null,null,"—"]
[null,"Change in fair value of warrant liability          ",null,null,"(42",")",null,"(2,545",")",null,"—",null,null,"—"]
[null,"Other income (expense), net",null,null,"(25",")",null,4,null,null,169,null,null,46]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Net loss",null,"$","(4,239",")","$","(6,921",")","$","(5,238",")","$","(9,690",")"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​  "]
[null,"Net loss per common share (basic and diluted)",null,"$","(12.24",")","$","(19.82",")","$","(0.34",")","$","(0.63",")"]
[null,"Weighted-average shares outstanding (basic and diluted)",null,null,346478,null,null,349170,null,null,15253704,null,null,15340713]

{"sheet":"The_Company_and_Basis_of_Prese1","index":24,"n_rows":45,"n_cols":2,"rows_kept":45,"cut":false,"hidden":false,"merged":[[37,0,39,0],[40,0,42,0],[43,0,45,0],[19,0,21,0],[22,0,24,0],[25,0,27,0],[28,0,30,0],[31,0,33,0],[34,0,36,0],[0,0,1,0],[3,0,6,0],[7,0,9,0],[10,0,12,0],[13,0,15,0],[16,0,18,0]]}
["The Company and Basis of Presentation (Policies)","12 Months Ended"]
[null,"Dec. 31, 2014"]
["The Company and Basis of Presentation"]
["Use of Estimates","Use of Estimates "]
[null,"        The preparation of financial statements in conformity with U.S. generally accepted accounting principles (“GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, expenses and related disclosures. Actual results could differ from those estimates. "]
[null,"        Prior to the completion of the IPO on July 1, 2013, the Company utilized significant estimates and assumptions in determining the fair value of its common stock. The Company utilized valuation methodologies in accordance with the framework of the 2004 American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its common stock. Each valuation methodology includes estimates and assumptions that require the Company's judgment. These estimates and assumptions include a number of objective and subjective factors, including external market conditions affecting the biotechnology industry sector, the prices at which the Company sold shares of its preferred stock, the superior rights and preferences of securities senior to its common stock at the time and the likelihood of achieving a liquidity event, such as an initial public offering or sale. Significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date."]
[]
["Cash and Cash Equivalents","Cash and Cash Equivalents "]
[null,"        The Company invests its excess cash in bank deposits, money market accounts, and short-term investments. The Company considers all highly liquid investments with an original maturity of 90 days or less at the time of purchase to be cash equivalents. Cash equivalents are reported at fair value."]
[]
["Investments","Investments "]
[null,"        Investments are considered to be available-for-sale and are carried at fair value. Unrealized gains and losses, if any, are reported as a separate component of stockholders' equity. The cost of investments classified as available-for-sale are adjusted for the amortization of premiums and accretion of discounts to maturity and recorded in other income (expense), net. Realized gains and losses, if any, are determined using the specific identification method and recorded in other income (expense), net. Investments with original maturities beyond 90 days at the date of purchase and which mature at, or less than twelve months from, the balance sheet date are classified as current. Investments with a maturity beyond twelve months from the balance sheet date are classified as long-term."]
[]
["Concentration of Credit Risk","Concentration of Credit Risk "]
[null,"        Cash, cash equivalents, and marketable securities consist of financial instruments that potentially subject the Company to concentrations of credit risk. The Company has established guidelines for investment of its excess cash and believes the guidelines maintain safety and liquidity through diversification of counterparties and maturities."]
[]
["Segment Information","Segment Information "]
[null,"        The Company views its operations and manages its business in one operating segment, which is the business of researching, developing and commercializing therapies for the treatment of patients with elevated levels of LDL-cholesterol and other cardiometabolic risk markers."]
[]
["Fair Value of Financial Instruments","Fair Value of Financial Instruments "]
[null,"        The Company's cash, cash equivalents and investments are carried at fair value. Financial instruments, including other prepaid and current assets, accounts payable and accrued liabilities are carried at cost, which approximates fair value. Debt is carried at amortized cost, which approximates fair value."]
[]
["Property and Equipment, Net","Property and Equipment, Net "]
[null,"        Property and equipment are recorded at cost, less accumulated depreciation. Depreciation is provided using the straight-line method over the estimated useful lives of the respective assets, generally three to ten years. Leasehold improvements are amortized over the lesser of the lease term or the estimated useful lives of the related assets."]
[]
["Impairment of Long-Lived Assets","Impairment of Long-Lived Assets "]
[null,"        The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. The impairment loss, if recognized, would be based on the excess of the carrying value of the impaired asset over its respective fair value. Excluding impairment losses recorded on assets held for sale, no other impairment losses have been recorded through December 31, 2014."]
[]
["Research and Development","Research and Development "]
[null,"        Research and development expenses consist of costs incurred to further the Company's research and development activities and include salaries and related benefits, costs associated with study studies, nonclinical activities (such as toxicology studies), regulatory activities, manufacturing activities to support clinical activities, research-related overhead expenses, and fees paid to external service providers that conduct certain research and development, clinical, and manufacturing activities on behalf of the Company. Research and development costs are expensed as incurred."]
[]
["In-Process Research and Development","In-Process Research and Development "]
[null,"        In April 2008, the Company acquired certain tangible research and development assets and intellectual property from Pfizer Inc. (“Pfizer”). As the acquired in-process research and development had not reached technological feasibility and had no alternative future uses in connection with this asset and intellectual property acquisition and the related purchase price allocation, the Company expensed $0.1 million as in-process research and development costs in 2008."]
[]
["Accrued Clinical Development Costs","Accrued Clinical Development Costs "]
[null,"        Outside research costs are a component of research and development expense. These expenses include fees paid to contract research organizations and other service providers that conduct certain clinical and product development activities on behalf of the Company. Depending upon the timing of payments to the service providers, the Company recognizes prepaid expenses or accrued expenses related to these costs. These accrued or prepaid expenses are based on management's estimates of the work performed under service agreements, milestones achieved and experience with similar contracts. The Company monitors each of these factors and adjusts estimates accordingly."]
[]
["Income Taxes","Income Taxes "]
[null,"        The Company utilizes the liability method of accounting for income taxes as required by ASC 740, Income Taxes. Under this method, deferred tax assets and liabilities are determined based on differences between financial reporting and the tax basis of assets and liabilities and are measured using enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company has incurred operating losses since inception. Accordingly, it is not more likely than not that the Company will realize deferred tax assets and as such, it has recorded a full valuation allowance."]
[]
["Warrants","Warrants "]
[null,"        The Company accounts for its warrants issued in connection with its various financing transactions based upon the characteristics and provisions of the instrument. Warrants classified as liabilities are recorded on the Company's balance sheet at their fair value on the date of issuance and are marked-to-market on each subsequent reporting period, with the fair value changes recognized in the statement of operations. Warrants classified as additional-paid-in-capital are recorded on the Company's balance sheet at their fair value on the date of issuance. The warrants are measured using the Black-Scholes option-pricing model subsequent to the pricing of the Company's IPO and a Monte Carlo valuation model for previous periods which are based, in part, upon inputs where there is little or no market data, requiring the Company to develop its own independent assumptions. (See Note 4)."]
[]
["Stock-Based Compensation","Stock-Based Compensation "]
[null,"        The Company accounts for stock-based compensation in accordance with the provisions of ASC 718, Compensation—Stock Compensation. Accordingly, compensation costs related to equity instruments granted are recognized over the requisite service periods of the awards on a straight-line basis at the grant-date fair value calculated using a Black-Scholes option pricing model. Additionally, under the provisions of ASC 718, the Company is required to include an estimate of the number of awards that will be forfeited in calculating compensation costs. Any changes to the estimated forfeiture rates are accounted for prospectively. Stock-based compensation arrangements with non-employees are recognized at the grant-date fair value and then re-measured at each reporting period. Expense is recognized during the period the related services are rendered."]

{"sheet":"The_Company_and_Basis_of_Prese2","index":25,"n_rows":15,"n_cols":6,"rows_kept":15,"cut":false,"hidden":false,"merged":[[0,0,1,0],[0,1,0,5],[1,1,1,5],[2,1,2,5],[3,0,16,0],[3,1,3,5],[4,1,4,5],[15,1,15,5],[16,1,16,5]]}
["The Company and Basis of Presentation (Tables) (Initial Public Offering)","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Initial Public Offering"]
["Summary of the Company's capitalization upon closing of its public offering"]
[]
[null,"Total common stock issued as of June 30, 2013",null,null,"396,414 "]
[null,"Conversion of Series A preferred stock into common stock upon closing of IPO",null,null,"8,244,781 "]
[null,"Conversion of Series A-1 preferred stock into common stock upon closing of IPO",null,null,"966,218 "]
[null,"Sales of common stock through IPO",null,null,"5,000,000 "]
[null,"​","​","​  ","​  ","​"]
[null,"Common stock issued as of July 1, 2013",null,null,"14,607,413 "]
[null,"Issuance of common stock to underwriters due to exercise of over-allotment",null,null,"750,000 "]
[null,"​","​","​  ","​  ","​"]
[null,"Total common stock issued as of July 11, 2013",null,null,"15,357,413 "]
[null,"​","​","​  ","​  ","​"]

{"sheet":"Debt_Tables","index":26,"n_rows":15,"n_cols":6,"rows_kept":15,"cut":false,"hidden":false,"merged":[[5,3,5,4],[0,0,1,0],[0,1,0,5],[1,1,1,5],[2,1,2,5],[3,0,16,0],[3,1,3,5],[4,1,4,5],[15,1,15,5],[16,1,16,5]]}
["Debt (Tables)","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Debt"]
["Schedule of estimated future principal payments due"]
[]
[null,"Years Ending December 31, ",null,"(in thousands) "]
[null,2014,null,"$","—"]
[null,2015,null,null,"638 "]
[null,2016,null,null,"1,604 "]
[null,2017,null,null,"1,709 "]
[null,2018,null,null,"1,049 "]
[null,"​","​","​  ","​  ","​"]
[null,"Total",null,"$","5,000 "]
[null,"​","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​  "]

{"sheet":"Commitments_and_contingencies_","index":27,"n_rows":14,"n_cols":18,"rows_kept":14,"cut":false,"hidden":false,"merged":[[14,1,14,17],[15,1,15,17],[6,17,7,17],[8,3,8,16],[0,0,1,0],[0,1,0,17],[1,1,1,17],[2,1,2,17],[3,0,15,0],[3,1,3,17],[4,1,4,17],[5,1,5,17],[6,8,7,8],[6,9,7,10],[6,11,7,11],[6,12,7,13],[6,14,7,14],[6,15,6,16],[7,15,7,16],[6,1,7,1],[6,2,7,2],[6,3,7,4],[6,5,7,5],[6,6,6,7],[7,6,7,7]]}
["Commitments and contingencies (Tables)","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Commitments and contingencies"]
["Summary of future minimum lease payments"]
[null,"The following table summarizes the Company's future minimum lease payments as of December 31, 2014: "]
[]
[null,null,null,"Total ",null,null,"Less than",null,null,"1 - 3 Years ",null,null,"3 - 5 Years ",null,null,"More than"]
[{"$nulls":6},"1 Year ",{"$nulls":8},"5 Years "]
[null,null,null,"(in thousands)"]
[null,"Operating lease",null,"$","552 ",null,"$","133 ",null,"$","251 ",null,"$","168 ",null,"$","—  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total",null,"$","552 ",null,"$","133 ",null,"$","251 ",null,"$","168 ",null,"$","—  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​  "]

{"sheet":"Property_and_Equipment_Tables","index":28,"n_rows":21,"n_cols":9,"rows_kept":21,"cut":false,"hidden":false,"merged":[[4,1,4,8],[21,1,21,8],[22,1,22,8],[5,3,5,7],[6,3,6,4],[6,6,6,7],[7,3,7,7],[0,0,1,0],[0,1,0,8],[1,1,1,8],[2,1,2,8],[3,0,22,0],[3,1,3,8]]}
["Property and Equipment (Tables)","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Property and Equipment"]
["Schedule of property and equipment"]
[]
[null,null,null,"December 31, "]
[null,null,null,2014,null,null,2013]
[null,null,null,"(in thousands)"]
[null,"Lab equipment",null,"$","519 ",null,"$","511 "]
[null,"Computer equipment",null,null,"110 ",null,null,"100 "]
[null,"Software",null,null,"74 ",null,null,"119 "]
[null,"Furniture and fixtures",null,null,"320 ",null,null,"11 "]
[null,"Leasehold improvements",null,null,"158 ",null,null,"21 "]
[null,"Assets in Progress",null,null,"2 ",null,null,"7 "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Subtotal",null,null,"1,183 ",null,null,"769 "]
[null,"Less accumulated depreciation and amortization",null,null,"403 ",null,null,"688 "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Property and equipment, net",null,"$","780 ",null,"$","81 "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​  "]

{"sheet":"Other_Accrued_Liabilities_Tabl","index":29,"n_rows":16,"n_cols":9,"rows_kept":16,"cut":false,"hidden":false,"merged":[[16,1,16,8],[17,1,17,8],[4,3,4,7],[5,3,5,4],[5,6,5,7],[6,3,6,7],[0,0,1,0],[0,1,0,8],[1,1,1,8],[2,1,2,8],[3,0,17,0],[3,1,3,8]]}
["Other Accrued Liabilities (Tables)","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Other Accrued Liabilities"]
["Schedule of other accrued liabilities"]
[null,null,null,"December 31, "]
[null,null,null,2014,null,null,2013]
[null,null,null,"(in thousands)"]
[null,"Accrued compensation",null,"$","313 ",null,"$","667 "]
[null,"Accrued professional fees",null,null,"167 ",null,null,"210 "]
[null,"Accrued franchise and property taxes",null,null,"107 ",null,null,"95 "]
[null,"Accrued interest",null,null,"104 ",null,null,"—"]
[null,"Accrued other",null,null,"144 ",null,null,"115 "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total other accrued liabilities",null,"$","835 ",null,"$","1,087 "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​  "]

{"sheet":"Investments_Tables","index":30,"n_rows":46,"n_cols":15,"rows_kept":46,"cut":false,"hidden":false,"merged":[[47,1,47,14],[0,0,1,0],[0,1,0,14],[1,1,1,14],[2,1,2,14],[3,0,47,0],[3,1,3,14],[4,1,4,14],[25,1,25,14],[26,1,26,14],[46,1,46,14],[28,11,30,11],[28,12,28,13],[29,12,29,13],[30,12,30,13],[28,14,30,14],[31,3,31,13],[29,6,29,7],[30,6,30,7],[28,8,30,8],[28,9,28,10],[29,9,29,10],[30,9,30,10],[6,14,8,14],[9,3,9,13],[27,3,27,13],[28,1,30,1],[28,2,30,2],[28,3,28,4],[29,3,29,4],[30,3,30,4],[28,5,30,5],[28,6,28,7],[6,8,8,8],[6,9,6,10],[7,9,7,10],[8,9,8,10],[6,11,8,11],[6,12,6,13],[7,12,7,13],[8,12,8,13],[5,3,5,13],[6,1,8,1],[6,2,8,2],[6,3,6,4],[7,3,7,4],[8,3,8,4],[6,5,8,5],[6,6,6,7],[7,6,7,7],[8,6,8,7]]}
["Investments (Tables)","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Investments"]
["Summary of the Company's cash equivalents and investments"]
[]
[null,null,null,"December 31, 2014 "]
[null,null,null,"Amortized",null,null,"Gross",null,null,"Gross",null,null,"Estimated"]
[null,null,null,"Cost ",null,null,"Unrealized",null,null,"Unrealized",null,null,"Fair"]
[{"$nulls":6},"Gains ",null,null,"Losses ",null,null,"Value "]
[null,null,null,"(in thousands)"]
[null,"Cash equivalents:"]
[null,"Money market funds",null,"$",357,null,"$","—",null,"$","—",null,"$",357]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Short-term investments:"]
[null,"Certificates of deposit",null,null,2934,null,null,"—",null,null,"—",null,null,2934]
[null,"U.S treasury notes",null,null,9020,null,null,4,null,null,"—",null,null,9024]
[null,"U.S. government agency securities",null,null,8853,null,null,"—",null,null,"(8",")",null,8845]
[null,"Long-term investments:"]
[null,"Certificates of deposit",null,null,1848,null,null,"—",null,null,"—",null,null,1848]
[null,"U.S. treasury notes",null,null,2494,null,null,"—",null,null,"(5",")",null,2489]
[null,"U.S. government agency securities",null,null,31454,null,null,"—",null,null,"(50",")",null,31404]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total",null,"$",56960,null,"$",4,null,"$","(63",")","$",56901]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​  "]
[]
[]
[null,null,null,"December 31, 2013 "]
[null,null,null,"Amortized",null,null,"Gross",null,null,"Gross",null,null,"Estimated"]
[null,null,null,"Cost ",null,null,"Unrealized",null,null,"Unrealized",null,null,"Fair"]
[{"$nulls":6},"Gains ",null,null,"Losses ",null,null,"Value "]
[null,null,null,"(in thousands)"]
[null,"Cash equivalents:"]
[null,"Money market funds",null,"$",5356,null,"$","—",null,"$","—",null,"$",5356]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Short-term investments:"]
[null,"U.S treasury notes",null,null,2071,null,null,"—",null,null,"—",null,null,2071]
[null,"U.S. government agency securities",null,null,1454,null,null,"—",null,null,"—",null,null,1454]
[null,"Long-term investments:"]
[null,"Certificates of deposit",null,null,238,null,null,"—",null,null,"—",null,null,238]
[null,"U.S. treasury notes",null,null,9116,null,null,3,null,null,"(2",")",null,9117]
[null,"U.S. government agency securities",null,null,8187,null,null,1,null,null,"(5",")",null,8183]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total",null,"$",26422,null,"$",4,null,"$","(7",")","$",26419]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​  "]

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["Fair Value Measurements (Tables)","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Fair Value Measurements"]
["Schedule of the Company's financial assets and liabilities that have been measured at fair value on a recurring basis"]
[]
[null,"Description ",null,"Total ",null,null,"Level 1 ",null,null,"Level 2 ",null,null,"Level 3 "]
[null,null,null,"(in thousands)"]
[null,"December 31, 2014"]
[null,"Assets:"]
[null,"Money market funds",null,"$","357 ",null,"$","357 ",null,"$","—",null,"$","—"]
[null,"Available-for-sale securities:"]
[null,"Certificates of deposit",null,null,"4,782 ",null,null,"4,782 ",null,null,"—",null,null,"—"]
[null,"U.S. treasury notes",null,null,"11,513 ",null,null,"11,513 ",null,null,"—",null,null,"—"]
[null,"U.S. government agency securities",null,null,"40,249 ",null,null,"—",null,null,"40,249 ",null,null,"—  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total assets at fair value",null,"$","56,901 ",null,"$","16,652 ",null,"$","40,249 ",null,"$","—  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​  "]
[null,"December 31, 2013"]
[null,"Assets:"]
[null,"Money market funds",null,"$","5,356 ",null,"$","5,356 ",null,"$","—",null,"$","—"]
[null,"Available-for-sale securities:"]
[null,"Certificates of deposit",null,null,"238 ",null,null,"238 ",null,null,"—",null,null,"—"]
[null,"U.S. treasury notes",null,null,"11,188 ",null,null,"11,188 ",null,null,"—",null,null,"—"]
[null,"U.S. government agency securities",null,null,"9,637 ",null,null,"—",null,null,"9,637 ",null,null,"—  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total assets at fair value",null,"$","26,419 ",null,"$","16,782 ",null,"$","9,637 ",null,"$","—  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​  "]

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["Stock Compensation (Tables)","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Stock Compensation"]
["Summary of activity relating to the Company's options to purchase common stock"]
[null,null,null,"Number of",null,null,"Weighted-Average",null,null,"Weighted-Average",null,null,"Aggregate"]
[null,null,null,"Options ",null,null,"Price",null,null,"Remaining",null,null,"Intrinsic"]
[{"$nulls":6},"Per Share ",null,null,"Contractual",null,null,"Value "]
[{"$nulls":9},"Term (Years) "]
[{"$nulls":12},"(in thousands)"]
[null,"Outstanding at December 31, 2013",null,null,1401101,null,"$",9.59,null,null,8.9499999999999993,null,"$",7755]
[null,"Granted",null,null,561500,null,"$",15.03]
[null,"Forfeited or expired (vested and unvested)",null,null,"(125,052",")","$",12.97]
[null,"Exercised",null,null,"(107,963",")","$",4.38]
[null,"​","​","​  ","​  ","​","​","​","​","​","​","​","​","​","​"]
[null,"Outstanding at December 31, 2014",null,null,1729586,null,"$",11.44,null,null,8.43,null,"$",50155]
[null,"​","​","​  ","​  ","​","​","​","​","​","​","​","​","​","​"]
[null,"​","​","​  ","​  ","​","​","​","​","​","​","​","​","​","​  "]
[]
[]
["Summary of information about the stock option plan"]
[]
[null,null,null,"Number of",null,null,"Weighted-Average",null,null,"Weighted-Average",null,null,"Aggregate"]
[null,null,null,"Options ",null,null,"Price",null,null,"Remaining",null,null,"Intrinsic"]
[{"$nulls":6},"Per Share ",null,null,"Contractual",null,null,"Value "]
[{"$nulls":9},"Term (Years) "]
[{"$nulls":12},"(in thousands)"]
[null,"Vested and expected to vest at December 31, 2014",null,null,"1,671,313 ",null,"$","11.37 ",null,null,"8.41 ",null,"$","48,588 "]
[null,"​","​","​  ","​  ","​","​","​","​","​","​","​","​","​","​"]
[null,"Exercisable at December 31, 2014",null,null,"752,397 ",null,"$","6.61 ",null,null,"7.58 ",null,"$","25,452 "]
[null,"​","​","​  ","​  ","​","​","​","​","​","​","​","​","​","​"]
[null,"​","​","​  ","​  ","​","​","​","​","​","​","​","​","​","​  "]
[]
[]
["Schedule of weighted-average assumptions used to compute the stock-based compensation costs for the stock options granted to employees and non-employees"]
[]
[null,null,null,"Year ended"]
[null,null,null,"December 31, "]
[null,null,null,2014,null,null,2013,null,null,2012]
[null,"Risk-free interest rate",null,null,"1.81 ","%",null,"1.45 ","%",null,"0.85 ","%"]
[null,"Dividend yield",null,null,"—",null,null,"—",null,null,"—"]
[null,"Weighted-average expected life of options (years)",null,null,"6.32 ",null,null,"6.26 ",null,null,"6.25 "]
[null,"Volatility",null,null,"75 ","%",null,"74 ","%",null,"80 ","%"]

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["Income Taxes (Tables)","12 Months Ended"]
[null,"Dec. 31, 2014"]
["Income Taxes"]
["Schedule of reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate"]
[]
[null,null,null,"December 31, "]
[null,null,null,2014,null,null,2013,null,null,2012]
[null,"Federal income tax (benefit) at statutory rate",null,null,"(34.0 ",")%",null,"(34.0 ",")%",null,"(34.0 ",")%"]
[null,"Change in Tax Rate",null,null,"2.1 ","%",null,"—","%",null,"—","%"]
[null,"Permanent items",null,null,"1.0 ","%",null,"4.9 ","%",null,"0.4 ","%"]
[null,"Other",null,null,"0.1 ","%",null,"—","%",null,"(0.2 ",")%"]
[null,"Change in valuation allowance",null,null,"30.8 ","%",null,"29.1 ","%",null,"33.8 ","%  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Effective income tax rate",null,null,"0.0 ","%",null,"0.0 ","%",null,"0.0 ","%  "]
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[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​  "]
[]
[]
["Schedule of significant components of the Company's deferred tax assets"]
[]
[null,null,null,"December 31, "]
[null,null,null,2014,null,null,2013]
[null,null,null,"(in thousands)"]
[null,"Deferred tax assets:"]
[null,"Federal and state operating loss carryforwards",null,"$",33099,null,"$",22485]
[null,"Equity Compensation",null,null,971,null,null,206]
[null,"Temporary differences",null,null,138,null,null,113]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total deferred tax assets",null,null,34208,null,null,22804]
[null,"Valuation allowance",null,null,"(34,208",")",null,"(22,804",")"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Net deferred tax assets",null,"$","—",null,"$","—  "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​  "]

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["Net Loss Per Common Share (Tables)","12 Months Ended"]
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["Net Loss Per Common Share"]
["Schedule of anti-dilutive securities excluded from the calculation of diluted net loss per share"]
[]
[null,null,null,"December 31,",null,null,"December 31,"]
[null,null,null,2014,null,null,2013]
[null,"Warrants for common stock",null,null,"285,920 ",null,null,"277,690 "]
[null,"Common shares under option",null,null,"1,729,586 ",null,null,"1,401,101 "]
[null,"Unvested restricted stock",null,null,"9,551 ",null,null,"16,703 "]
[null,"​","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total potential dilutive shares",null,null,"2,025,057 ",null,null,"1,695,494 "]
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["Selected Quarterly Financial Data (Unaudited)"]
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[null,null,null,"March 31 ",null,null,"June 30 ",null,null,"September 30 ",null,null,"December 31 "]
[null,null,null,"(in thousands, except share and per share data)"]
[null,"Operating expenses:"]
[null,"Research and development",null,"$",5400,null,"$",6528,null,"$",7174,null,"$",6200]
[null,"General and administrative",null,null,2490,null,null,2726,null,null,2526,null,null,3180]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total operating expenses",null,null,7890,null,null,9254,null,null,9700,null,null,9380]
[null,"Loss from operations:",null,null,"(7,890",")",null,"(9,254",")",null,"(9,700",")",null,"(9,380",")"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Interest expense",null,null,"—",null,null,"(1",")",null,"(135",")",null,"(134",")"]
[null,"Change in fair value of warrant liability",null,null,"—",null,null,"—",null,null,"—",null,null,"—"]
[null,"Other income (expense), net",null,null,16,null,null,17,null,null,29,null,null,57]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Net loss",null,"$","(7,874",")","$","(9,238",")","$","(9,806",")","$","(9,457",")"]
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[null,"Net loss per common share (basic and diluted)",null,"$","(0.51",")","$","(0.60",")","$","(0.64",")","$","(0.49",")"]
[null,"Weighted-average shares outstanding (basic and diluted)",null,null,15369055,null,null,15399018,null,null,15432641,null,null,19276639]
[]
[]
[null,null,null,2013]
[null,null,null,"March 31 ",null,null,"June 30 ",null,null,"September 30 ",null,null,"December 31 "]
[null,"Operating expenses:"]
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[null,"General and administrative",null,null,1251,null,null,1172,null,null,1924,null,null,2398]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Total operating expenses",null,null,3344,null,null,4272,null,null,5407,null,null,9736]
[null,"Loss from operations:",null,null,"(3,344",")",null,"(4,272",")",null,"(5,407",")",null,"(9,736",")"]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Interest expense",null,null,"(828",")",null,"(108",")",null,"—",null,null,"—"]
[null,"Change in fair value of warrant liability          ",null,null,"(42",")",null,"(2,545",")",null,"—",null,null,"—"]
[null,"Other income (expense), net",null,null,"(25",")",null,4,null,null,169,null,null,46]
[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​"]
[null,"Net loss",null,"$","(4,239",")","$","(6,921",")","$","(5,238",")","$","(9,690",")"]
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[null,"​","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​","​  ","​  ","​  "]
[null,"Net loss per common share (basic and diluted)",null,"$","(12.24",")","$","(19.82",")","$","(0.34",")","$","(0.63",")"]
[null,"Weighted-average shares outstanding (basic and diluted)",null,null,346478,null,null,349170,null,null,15253704,null,null,15340713]

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["Initial Public Offering | Common stock"]
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["Over-allotment option"]
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["Summary of Significant Accounting Policies (Details) (USD $)","12 Months Ended"]
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{"sheet":"Debt_Details","index":39,"n_rows":98,"n_cols":16,"rows_kept":98,"cut":false,"hidden":false,"merged":[[0,0,1,0],[0,5,0,6]]}
["Debt (Details) (USD $)","12 Months Ended","0 Months Ended","1 Months Ended","4 Months Ended","12 Months Ended",null,"0 Months Ended","1 Months Ended"]
[null,"Dec. 31, 2013","Feb. 28, 2013","Feb. 28, 2013","Dec. 31, 2012","Dec. 31, 2014","Dec. 31, 2012","Jul. 02, 2013","Jun. 30, 2014","Apr. 19, 2013","Dec. 31, 2011","Jan. 31, 2012","Nov. 30, 2012","Sep. 30, 2012","2013-05-29","Apr. 28, 2008"]
["Debt"]
["Deferred financing costs",{"$nulls":4},100000]
["Series A preferred stock"]
["Estimated future principal payments due under the Credit Facility"]
["Conversion of convertible promissory notes into Series A preferred stock (in shares)",16623092]
["Preferred stock, shares issued",null,null,null,23975000,null,23975000,null,null,null,23975000]
["Share price of preferred stock (in dollars per share)",{"$nulls":8},1]
["Number of shares of preferred stock converted into shares of common stock",-57598092]
["Series A-1 preferred stock"]
["Estimated future principal payments due under the Credit Facility"]
["Conversion of convertible promissory notes into Series A preferred stock (in shares)",6750000]
["Number of shares of preferred stock converted into shares of common stock",-6750000]
["Warrant"]
["Debt"]
["Exercise price (in dollars per share)",{"$nulls":4},7.23]
["Series A preferred stock warrant"]
["Debt"]
["Warrants exercisable into stock (in shares)",{"$nulls":6},1940000]
["Exercise price (in dollars per share)",{"$nulls":6},1]
["10% Convertible promissory notes | Series A preferred stock"]
["Estimated future principal payments due under the Credit Facility"]
["Aggregate principal amount",null,15700000,15700000]
["Accrued interest",null,900000,900000]
["Conversion of convertible promissory notes into Series A preferred stock (in shares)",null,16623092,16623092]
["Conversion price (in dollars per share)",null,1,1]
["Short term convertible notes issued January 2012"]
["Debt"]
["Interest rate (as a percent)",{"$nulls":10},0.1]
["Estimated future principal payments due under the Credit Facility"]
["Aggregate principal amount",{"$nulls":10},6000000]
["Short term convertible notes issued September and November 2012"]
["Debt"]
["Interest rate (as a percent)",{"$nulls":11},0.1]
["Estimated future principal payments due under the Credit Facility"]
["Aggregate principal amount",{"$nulls":11},9700000]
["Short term borrowings with related parties, net of debt discount",{"$nulls":11},9400000]
["Short term convertible notes issued September and November 2012 | Series A preferred stock warrant | Series A preferred stock"]
["Estimated future principal payments due under the Credit Facility"]
["Aggregate purchase price of warrants",null,null,null,9700]
["Short term convertible notes issued September and November 2012 | Series A preferred stock warrant | Total"]
["Estimated future principal payments due under the Credit Facility"]
["Estimated fair value of warrants",{"$nulls":11},300000]
["Short term convertible notes issued September 2012"]
["Estimated future principal payments due under the Credit Facility"]
["Fair value of beneficial conversion feature",null,null,300000]
["Short term convertible notes issued September 2012 | Interest Expense."]
["Estimated future principal payments due under the Credit Facility"]
["Amortization of debt discount and beneficial conversion",200000,null,null,null,200000,100000]
["Short term convertible notes issued September 2012 | Warrant | Total"]
["Estimated future principal payments due under the Credit Facility"]
["Estimated fair value of warrants",{"$nulls":12},100000]
["Pfizer note"]
["Debt"]
["Interest rate (as a percent)",{"$nulls":14},8.9300000000000004E-2]
["Estimated future principal payments due under the Credit Facility"]
["Aggregate principal amount",{"$nulls":14},5000000]
["Outstanding principal amount",{"$nulls":13},7800000]
["Accrued interest during period",300000,{"$nulls":4},600000]
["Pfizer note | Series A-1 preferred stock"]
["Estimated future principal payments due under the Credit Facility"]
["Preferred stock, shares issued",{"$nulls":13},6750000]
["Share price of preferred stock (in dollars per share)",{"$nulls":13},1.1559999999999999]
["Number of shares of preferred stock converted into shares of common stock",{"$nulls":6},966218]
["Credit Facility"]
["Debt"]
["Maximum borrowing capacity",{"$nulls":4},20000000]
["Percentage of final payment equal to amount drawn under the Credit Facility",{"$nulls":4},0.08]
["Estimated future principal payments due under the Credit Facility"]
[2015,{"$nulls":4},638000]
[2016,{"$nulls":4},1604000]
[2017,{"$nulls":4},1709000]
[2018,{"$nulls":4},1049000]
["Total",{"$nulls":4},5000000]
["Interest expense",{"$nulls":4},300000]
["Interest payments",{"$nulls":4},100000]
["Term A Loan"]
["Debt"]
["Maximum borrowing capacity",{"$nulls":4},5000000]
["Period of consecutive equal monthly installments of principal and interest",{"$nulls":4},"36 months"]
["Interest rate (as a percent)",{"$nulls":4},6.4000000000000001E-2]
["Term A Loan | Warrant"]
["Debt"]
["Warrants exercisable into stock (in shares)",{"$nulls":7},8230]
["Exercise price (in dollars per share)",{"$nulls":7},15.19]
["Unamortized discount",{"$nulls":7},100000]
["Term A Loan | Secured promissory notes"]
["Debt"]
["Proceeds from issuance of debt",{"$nulls":7},5000000]
["Term B Loan"]
["Debt"]
["Maximum borrowing capacity",{"$nulls":4},15000000]
["Remaining borrowing capacity",{"$nulls":4},15000000]
["Interest rate (as a percent)",{"$nulls":4},6.4000000000000001E-2]
["Reference rate",{"$nulls":4},"three month LIBOR"]
["Number of business days prior to funding of new term loan",{"$nulls":4},"3 days"]
["Interest rate margin (as a percent)",{"$nulls":4},6.1699999999999998E-2]

{"sheet":"Warrants_Details","index":40,"n_rows":30,"n_cols":10,"rows_kept":30,"cut":false,"hidden":false,"merged":[[0,0,1,0],[0,1,0,2],[0,3,0,4]]}
["Warrants (Details) (USD $)","3 Months Ended",null,"12 Months Ended"]
[null,"Jun. 30, 2013","Mar. 31, 2013","Dec. 31, 2013","Dec. 31, 2012","Dec. 31, 2014","Sep. 30, 2012","Nov. 30, 2012","Jul. 02, 2013","Jun. 30, 2014"]
["Warrants"]
["(Loss)/gain recognized for change in the fair value of the warrant liability",-2545000,-42000,-2587000,32000]
["Warrant"]
["Warrants"]
["Exercise price (in dollars per share)",{"$nulls":4},7.23]
["Number of shares of common stock to be purchased against outstanding warrants",{"$nulls":4},285920]
["Warrant | Total | Short term convertible notes issued September 2012"]
["Warrants"]
["Estimated fair value",{"$nulls":5},100000]
["Warrant | Total | Short term convertible notes issued November 2012"]
["Warrants"]
["Estimated fair value",{"$nulls":6},200000]
["Series A preferred stock warrant"]
["Warrants"]
["Warrants exercisable into stock (in shares)",{"$nulls":7},1940000]
["Exercise price (in dollars per share)",{"$nulls":7},1]
["Number of shares of common stock to be purchased against outstanding warrants",{"$nulls":4},277690]
["Series A preferred stock warrant | Total | Short term convertible notes issued September and November 2012"]
["Warrants"]
["Estimated fair value",{"$nulls":6},300000]
["Common stock"]
["Warrants"]
["Exercise price (in dollars per share)",{"$nulls":8},15.19]
["Common stock | Warrant"]
["Warrants"]
["Warrants exercisable into stock (in shares)",{"$nulls":7},277690,8230]
["Fair value of warrants",{"$nulls":8},100000]
["Share price of common stock (in dollars per share)",{"$nulls":7},6.99]

{"sheet":"Commitments_and_contingencies_1","index":41,"n_rows":26,"n_cols":6,"rows_kept":26,"cut":false,"hidden":false,"merged":[[0,0,3,0],[0,2,0,4],[1,1,3,1],[1,2,3,2],[1,3,3,3],[1,4,3,4]]}
["Commitments and contingencies (Details) (USD $)","1 Months Ended","12 Months Ended",null,null,"1 Months Ended"]
[null,"Feb. 28, 2014","Dec. 31, 2014","Dec. 31, 2013","Dec. 31, 2012","2014-05-31"]
[{"$nulls":5},"item"]
[{"$nulls":5},"sqft"]
["Commitments and contingencies"]
["Term period of lease","63 months"]
["Operating lease period for monthly rent increasing in fixed monthly rent","12 months"]
["Operating lease period after which monthly rent increase","3 months"]
["Operating leases"]
["Total",null,552000]
["Less than 1 Year",null,133000]
["1-3 Years",null,251000]
["3-5 Years",null,168000]
["Total"]
["Total",null,552000]
["Less than 1 Year",null,133000]
["1-3 Years",null,251000]
["3-5 Years",null,168000]
["Rent expense",null,300000,300000,300000]
["Third amendment to the operating lease agreement for laboratory facility in Plymouth, Michigan"]
["Commitments and contingencies"]
["Adjusted rentable laboratory space (in square feet)",{"$nulls":4},3045]
["Adjusted proportionate share of landlord's expenses and taxes (as a percent)",{"$nulls":4},7.3999999999999996E-2]
["Number of terms which Company may exercise to renew lease",{"$nulls":4},1]
["Lease renewal term",{"$nulls":4},"3 years"]
["Annual base rent under new lease agreement",{"$nulls":4},37000]

{"sheet":"Commitments_and_contingencies_2","index":42,"n_rows":7,"n_cols":2,"rows_kept":7,"cut":false,"hidden":false,"merged":[[0,0,1,0]]}
["Commitments and contingencies (Details 2) (License agreement., USD $)","12 Months Ended"]
[null,"Dec. 31, 2014"]
["License agreement"]
["Milestone minimum annual payment",50000]
["Maximum"]
["License agreement"]
["Number of shares of common stock to be issued upon meeting various future milestones",11451]

{"sheet":"Property_and_Equipment_Detail","index":43,"n_rows":25,"n_cols":4,"rows_kept":25,"cut":false,"hidden":false,"merged":[[0,1,0,3]]}
["Property and Equipment (Detail) (USD $)","12 Months Ended"]
["In Thousands, unless otherwise specified","Dec. 31, 2014","Dec. 31, 2013","Dec. 31, 2012"]
["Property and Equipment"]
["Property and equipment, gross",1183,769]
["Less accumulated depreciation and amortization",403,688]
["Property and equipment, net",780,81]
["Depreciation expense",160,71,139]
["Lab equipment"]
["Property and Equipment"]
["Property and equipment, gross",519,511]
["Computer equipment"]
["Property and Equipment"]
["Property and equipment, gross",110,100]
["Software"]
["Property and Equipment"]
["Property and equipment, gross",74,119]
["Furniture and fixtures"]
["Property and Equipment"]
["Property and equipment, gross",320,11]
["Leasehold improvements"]
["Property and Equipment"]
["Property and equipment, gross",158,21]
["Assets in Progress"]
["Property and Equipment"]
["Property and equipment, gross",2,7]

{"sheet":"Other_Accrued_Liabilities_Deta","index":44,"n_rows":9,"n_cols":3,"rows_kept":9,"cut":false,"hidden":false,"merged":[[0,1,1,1],[0,2,1,2]]}
["Other Accrued Liabilities (Detail) (USD $)","Dec. 31, 2014","Dec. 31, 2013"]
["In Thousands, unless otherwise specified"]
["Other Accrued Liabilities"]
["Accrued compensation",313,667]
["Accrued professional fees",167,210]
["Accrued franchise and property taxes",107,95]
["Accrued interest",104]
["Accrued other",144,115]
["Total other accrued liabilities",835,1087]

{"sheet":"Investments_Details","index":45,"n_rows":44,"n_cols":12,"rows_kept":44,"cut":false,"hidden":false,"merged":[[0,0,1,0],[0,1,0,8],[0,9,0,11]]}
["Investments (Details) (USD $)","3 Months Ended",{"$nulls":7},"12 Months Ended"]
[null,"Dec. 31, 2014","Sep. 30, 2014","Jun. 30, 2014","Mar. 31, 2014","Dec. 31, 2013","Sep. 30, 2013","Jun. 30, 2013","Mar. 31, 2013","Dec. 31, 2014","Dec. 31, 2013","Dec. 31, 2012"]
["Cash equivalents and investments"]
["Gross Unrealized Gains",4000,null,null,null,4000,null,null,null,4000,4000]
["Gross Unrealized Losses",-63000,null,null,null,-7000,null,null,null,-63000,-7000]
["Total, Amortized Cost",56960000,null,null,null,26422000,null,null,null,56960000,26422000]
["Total, Estimated Fair Value",56901000,null,null,null,26419000,null,null,null,56901000,26419000]
["Other income (expense), net",57000,29000,17000,16000,46000,169000,4000,-25000,119000,194000,-84000]
["Reclassification out of accumulated other comprehensive income (loss)"]
["Cash equivalents and investments"]
["Other income (expense), net",{"$nulls":8},0]
["Short-term investments. | U.S. treasury notes"]
["Cash equivalents and investments"]
["Investments, Amortized Cost",9020000,null,null,null,2071000,null,null,null,9020000,2071000]
["Gross Unrealized Gains",4000,{"$nulls":7},4000]
["Investments, Estimated Fair Value",9024000,null,null,null,2071000,null,null,null,9024000,2071000]
["Short-term investments. | U.S. government agency securities"]
["Cash equivalents and investments"]
["Investments, Amortized Cost",8853000,null,null,null,1454000,null,null,null,8853000,1454000]
["Gross Unrealized Losses",-8000,{"$nulls":7},-8000]
["Investments, Estimated Fair Value",8845000,null,null,null,1454000,null,null,null,8845000,1454000]
["Long-term investments | U.S. treasury notes"]
["Cash equivalents and investments"]
["Investments, Amortized Cost",2494000,null,null,null,9116000,null,null,null,2494000,9116000]
["Gross Unrealized Gains",{"$nulls":4},3000,{"$nulls":4},3000]
["Gross Unrealized Losses",-5000,null,null,null,-2000,null,null,null,-5000,-2000]
["Investments, Estimated Fair Value",2489000,null,null,null,9117000,null,null,null,2489000,9117000]
["Long-term investments | U.S. government agency securities"]
["Cash equivalents and investments"]
["Investments, Amortized Cost",31454000,null,null,null,8187000,null,null,null,31454000,8187000]
["Gross Unrealized Gains",{"$nulls":4},1000,{"$nulls":4},1000]
["Gross Unrealized Losses",-50000,null,null,null,-5000,null,null,null,-50000,-5000]
["Investments, Estimated Fair Value",31404000,null,null,null,8183000,null,null,null,31404000,8183000]
["Money market funds"]
["Cash equivalents and investments"]
["Cash equivalents, Estimated Fair Value",357000,null,null,null,5356000,null,null,null,357000,5356000]
["Certificates of deposit | Short-term investments."]
["Cash equivalents and investments"]
["Investments, Amortized Cost",2934000,{"$nulls":7},2934000]
["Investments, Estimated Fair Value",2934000,{"$nulls":7},2934000]
["Certificates of deposit | Long-term investments"]
["Cash equivalents and investments"]
["Investments, Amortized Cost",1848000,null,null,null,238000,null,null,null,1848000,238000]
["Investments, Estimated Fair Value",1848000,null,null,null,238000,null,null,null,1848000,238000]

{"sheet":"Fair_Value_Measurements_Detail","index":46,"n_rows":56,"n_cols":4,"rows_kept":56,"cut":false,"hidden":false,"merged":[[0,0,1,0],[0,1,0,3]]}
["Fair Value Measurements (Details) (USD $)","12 Months Ended"]
[null,"Dec. 31, 2014","Dec. 31, 2013","Dec. 31, 2012"]
["Assets:"]
["Total, Estimated Fair Value",56901000,26419000]
["Transfer of assets between levels",0,0]
["Transfer of liabilities between levels",null,0,0]
["U.S. treasury notes"]
["Assets:"]
["Available for sale securities",null,11188000]
["U.S. government agency securities"]
["Assets:"]
["Available for sale securities",null,9637000]
["Certificates of deposit"]
["Assets:"]
["Available for sale securities",null,238000]
["Level 1 | U.S. treasury notes"]
["Assets:"]
["Available for sale securities",null,11188000]
["Level 1 | Certificates of deposit"]
["Assets:"]
["Available for sale securities",null,238000]
["Level 2"]
["Assets:"]
["Total, Estimated Fair Value",null,9637000]
["Level 2 | U.S. government agency securities"]
["Assets:"]
["Available for sale securities",null,9637000]
["Recurring fair value measurement | Level 1"]
["Assets:"]
["Money market fund",357000,5356000]
["Total, Estimated Fair Value",16652000,16782000]
["Recurring fair value measurement | Level 1 | U.S. treasury notes"]
["Assets:"]
["Available for sale securities",11513000]
["Recurring fair value measurement | Level 1 | Certificates of deposit"]
["Assets:"]
["Available for sale securities",4782000]
["Recurring fair value measurement | Level 2"]
["Assets:"]
["Total, Estimated Fair Value",40249000]
["Recurring fair value measurement | Level 2 | U.S. government agency securities"]
["Assets:"]
["Available for sale securities",40249000]
["Recurring fair value measurement | Total"]
["Assets:"]
["Money market fund",357000,5356000]
["Total, Estimated Fair Value",56901000,26419000]
["Recurring fair value measurement | Total | U.S. treasury notes"]
["Assets:"]
["Available for sale securities",11513000]
["Recurring fair value measurement | Total | U.S. government agency securities"]
["Assets:"]
["Available for sale securities",40249000]
["Recurring fair value measurement | Total | Certificates of deposit"]
["Assets:"]
["Available for sale securities",4782000]

{"sheet":"Fair_Value_Measurements_Detail1","index":47,"n_rows":7,"n_cols":4,"rows_kept":7,"cut":false,"hidden":false,"merged":[[0,1,0,3]]}
["Fair Value Measurements (Details 2) (Nonrecurring fair value measurement, USD $)","12 Months Ended"]
["In Millions, unless otherwise specified","Dec. 31, 2014","Dec. 31, 2012","Dec. 31, 2013"]
["Fair Value Measurements on a Nonrecurring Basis"]
["Impairment loss related to the assets held for sale",0,0.1]
["Maximum"]
["Fair Value Measurements on a Nonrecurring Basis"]
["Impairment loss related to the assets held for sale",null,null,0.1]

{"sheet":"Convertible_Preferred_Stock_an1","index":48,"n_rows":56,"n_cols":10,"rows_kept":56,"cut":false,"hidden":false,"merged":[[0,0,1,0],[0,2,0,3]]}
["Convertible Preferred Stock and Stockholders' Equity (Details) (USD $)","12 Months Ended","0 Months Ended",null,"1 Months Ended","0 Months Ended"]
[null,"Dec. 31, 2013","Apr. 19, 2013","Feb. 28, 2013","Feb. 28, 2013","Jul. 02, 2013","2013-05-29","Apr. 28, 2008","Jan. 31, 2012","Nov. 30, 2012"]
["Convertible preferred stock and stockholders' deficit"]
["Proceeds from issuance of preferred stock, net of issuance costs",16824000]
["Pfizer note"]
["Convertible preferred stock and stockholders' deficit"]
["Interest rate (as a percent)",{"$nulls":6},8.9300000000000004E-2]
["Aggregate principal amount",{"$nulls":6},5000000]
["Outstanding principal amount",{"$nulls":5},7800000]
["Short term convertible notes issued January 2012"]
["Convertible preferred stock and stockholders' deficit"]
["Interest rate (as a percent)",{"$nulls":7},0.1]
["Aggregate principal amount",{"$nulls":7},6000000]
["Short term convertible notes issued September and November 2012"]
["Convertible preferred stock and stockholders' deficit"]
["Interest rate (as a percent)",{"$nulls":8},0.1]
["Aggregate principal amount",{"$nulls":8},9700000]
["Common stock | Warrant"]
["Convertible preferred stock and stockholders' deficit"]
["Share price of preferred stock (in dollars per share)",{"$nulls":4},6.99]
["Series A preferred stock"]
["Convertible preferred stock and stockholders' deficit"]
["Conversion of convertible promissory notes into Series A preferred stock (in shares)",16623092]
["Preferred stock, shares authorized",null,17000000]
["Share price of preferred stock (in dollars per share)",null,1]
["Proceeds from issuance of preferred stock, net of issuance costs",null,16900000]
["Stock issuance costs",-120000,100000]
["Conversion rate",null,0.14299999999999999]
["Number of shares of convertible preferred stock converted into common stock",-57598092]
["Series A preferred stock | 10% Convertible promissory notes"]
["Convertible preferred stock and stockholders' deficit"]
["Aggregate principal amount",null,null,15700000,15700000]
["Accrued interest",null,null,900000,900000]
["Conversion of convertible promissory notes into Series A preferred stock (in shares)",null,null,16623092,16623092]
["Conversion price (in dollars per share)",null,null,1,1]
["Conversion rate",null,null,0.14299999999999999,0.14299999999999999]
["Series A-1 preferred stock"]
["Convertible preferred stock and stockholders' deficit"]
["Conversion of convertible promissory notes into Series A preferred stock (in shares)",6750000]
["Stock issuance costs",53000]
["Number of shares of convertible preferred stock converted into common stock",-6750000]
["Series A-1 preferred stock | Pfizer note"]
["Convertible preferred stock and stockholders' deficit"]
["Preferred stock, shares authorized",{"$nulls":5},6750000]
["Share price of preferred stock (in dollars per share)",{"$nulls":5},1.1559999999999999]
["Conversion rate",{"$nulls":5},0.14299999999999999]
["Number of shares of convertible preferred stock converted into common stock",{"$nulls":4},966218]
["Initial Public Offering | Common stock"]
["Convertible preferred stock and stockholders' deficit"]
["Number of shares of convertible preferred stock converted into common stock",{"$nulls":4},9210999]
["Initial Public Offering | Series A preferred stock"]
["Convertible preferred stock and stockholders' deficit"]
["Number of shares of convertible preferred stock converted into common stock",{"$nulls":4},8244781]
["Initial Public Offering | Series A-1 preferred stock"]
["Convertible preferred stock and stockholders' deficit"]
["Number of shares of convertible preferred stock converted into common stock",{"$nulls":4},966218]

{"sheet":"Stock_Compensation_Details","index":49,"n_rows":51,"n_cols":5,"rows_kept":51,"cut":false,"hidden":false,"merged":[[0,0,1,0],[0,1,0,3]]}
["Stock Compensation (Details) (USD $)","12 Months Ended",null,null,"0 Months Ended"]
[null,"Dec. 31, 2014","Dec. 31, 2013","Dec. 31, 2012","Jun. 25, 2013"]
["Number of Options"]
["Outstanding at the beginning of period (in shares)",1401101]
["Granted (in shares)",561500]
["Forfeited or expired (vested and unvested) (in shares)",-125052]
["Exercised (in shares)",-107963]
["Outstanding at the end of the period (in shares)",1729586,1401101]
["Weighted-Average Price Per Share"]
["Outstanding at the beginning of period (in dollars per share)",9.59]
["Granted (in dollars per share)",15.03]
["Forfeited or expired (vested and unvested) (in dollars per share)",12.97]
["Exercised (in dollars per share)",4.38]
["Outstanding at the end of the period (in dollars per share)",11.44,9.59]
["Weighted-Average Remaining Contractual Term (Years)"]
["Outstanding at the end of the period","8 years 5 months 5 days","8 years 11 months 12 days"]
["Aggregate Intrinsic Value"]
["Outstanding at the end of the period (in dollars)",50155000,7755000]
["Information about the stock option plan"]
["Number of Options, vested and expected to vest (in shares)",1671313]
["Number of Options, exercisable (in shares)",752397]
["Weighted-Average Price Per Share, vested and expected to vest (in dollars per share)",11.37]
["Weighted-Average Price Per Share, exercisable (in dollars per share)",6.61]
["Weighted-Average Remaining Contractual Term, vested and expected to vest","8 years 4 months 28 days"]
["Weighted-Average Remaining Contractual Term, exercisable","7 years 6 months 29 days"]
["Aggregate Intrinsic Value, vested and expected to vest (in dollars)",48588000]
["Aggregate Intrinsic Value, exercisable (in dollars)",25452000]
["Total intrinsic value of stock options exercised",1400000,200000,100000]
["Additional disclosures"]
["Unrecognized compensation cost (in dollars)",9300000]
["Weighted-average period over which remaining unrecognized compensation cost will be recognized","2 years 10 months 24 days"]
["Weighted-average grant-date fair value (in dollars per share)",10.15,7.14,1.33]
["Stock-based compensation expense",3700000,1200000,100000]
["Assumptions used to compute the share-based compensation costs for stock options granted to employees and non-employees"]
["Risk-free interest rate (as a percent)",1.8100000000000002E-2,1.4500000000000001E-2,8.5000000000000006E-3]
["Weighted-average expected life of options (years)","6 years 3 months 26 days","6 years 3 months 4 days","6 years 3 months"]
["Volatility (as a percent)",0.75,0.74,0.8]
["2013 Stock Option and Incentive Plan"]
["Stock compensation"]
["Shares reserved and approved for issuance",null,null,null,1100000]
["Shares reserved under previous plan and subsequently transferred to new plan",null,null,null,54129]
["Percentage of increase in the number of shares reserved and available for issuance",null,null,null,2.5000000000000001E-2]
["2008 Incentive Stock Option and Restricted Stock Plan"]
["Stock compensation"]
["Shares reserved under previous plan and subsequently transferred to new plan",null,null,null,54129]
["Expiration period","10 years"]
["Period from cessation of employment within which options expire if not exercised","90 days"]
["Grant period of stock awards","10 years"]
["Purchase price expressed as a percentage of fair value of shares on the date of grant",1]
["Vesting percentage on the first anniversary of the option grant",0.25]
["Period for which remainder of grant amount will vest on the first day of each calendar quarter","3 years"]

{"sheet":"Employee_Benefit_Plan_Details","index":50,"n_rows":4,"n_cols":4,"rows_kept":4,"cut":false,"hidden":false,"merged":[[0,0,1,0],[0,1,0,3]]}
["Employee Benefit Plan (Details) (USD $)","12 Months Ended"]
[null,"Dec. 31, 2014","Dec. 31, 2013","Dec. 31, 2012"]
["Employee Benefit Plan"]
["Contributions to the 401(k) Plan",0,0,0]

{"sheet":"Income_Taxes_Details","index":51,"n_rows":13,"n_cols":4,"rows_kept":13,"cut":false,"hidden":false,"merged":[[0,0,1,0],[0,1,0,3]]}
["Income Taxes (Details) (USD $)","12 Months Ended"]
[null,"Dec. 31, 2014","Dec. 31, 2013","Dec. 31, 2012"]
["Income Taxes"]
["Provision for income taxes",0,0,0]
["Deferred tax assets, before valuation allowance",34208000,22804000,14400000]
["Net operating loss carryforwards"]
["NOLs related to excess tax benefits",500000]
["Federal"]
["Net operating loss carryforwards"]
["Net operating loss carryforwards",95100000,62300000,40500000]
["State"]
["Net operating loss carryforwards"]
["Net operating loss carryforwards",16600000,33100000,11300000]

{"sheet":"Income_Taxes_Detail_2","index":52,"n_rows":10,"n_cols":4,"rows_kept":10,"cut":false,"hidden":false,"merged":[[0,0,1,0],[0,1,0,3]]}
["Income Taxes (Detail 2) (USD $)","12 Months Ended"]
[null,"Dec. 31, 2014","Dec. 31, 2013","Dec. 31, 2012"]
["Reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate"]
["Federal income tax (benefit) at statutory rate",-0.34,-0.34,-0.34]
["Change in Tax Rate",2.1000000000000001E-2]
["Permanent items",0.01,4.9000000000000002E-2,4.0000000000000001E-3]
["Other",1E-3,null,-2E-3]
["Change in valuation allowance",0.308,0.29099999999999998,0.33800000000000002]
["Effective income tax rate",0,0,0]
["Unrecognized tax benefits related to interest and penalties accrued",0]

{"sheet":"Income_Taxes_Detail_3","index":53,"n_rows":8,"n_cols":4,"rows_kept":8,"cut":false,"hidden":false,"merged":[[0,1,1,1],[0,2,1,2],[0,3,1,3]]}
["Income Taxes (Detail 3) (USD $)","Dec. 31, 2014","Dec. 31, 2013","Dec. 31, 2012"]
["In Thousands, unless otherwise specified"]
["Deferred tax assets:"]
["Federal and state operating loss carryforwards",33099,22485]
["Equity Compensation",971,206]
["Temporary differences",138,113]
["Total deferred tax assets",34208,22804,14400]
["Valuation allowance",-34208,-22804]

{"sheet":"License_Agreement_Details","index":54,"n_rows":12,"n_cols":5,"rows_kept":12,"cut":false,"hidden":false,"merged":[[0,0,1,0],[0,2,0,4]]}
["License Agreement (Details) (License agreement., USD $)","1 Months Ended","12 Months Ended"]
[null,"Dec. 31, 2011","Dec. 31, 2014","Dec. 31, 2013","Dec. 31, 2012"]
["License agreement"]
["Number of shares of common stock issued under agreement",2862]
["License issue fee",50000]
["Fair value of common stock",4400]
["Milestone minimum annual payment",null,50000]
["Payment due period following achievement of milestone",null,"30 days"]
["Expenses recognized that are associated with the license agreement",null,50000,50000,50000]
["Maximum"]
["License agreement"]
["Number of shares of common stock to be issued upon meeting various future milestones",null,11451]

{"sheet":"Net_Loss_Per_Common_Share_Deta","index":55,"n_rows":15,"n_cols":4,"rows_kept":15,"cut":false,"hidden":false,"merged":[[0,0,1,0],[0,2,0,3]]}
["Net Loss Per Common Share (Details)","0 Months Ended","12 Months Ended"]
[null,"Jun. 11, 2013","Dec. 31, 2014","Dec. 31, 2013"]
["Net Loss Per Common Share"]
["Reverse stock split ratio of shares outstanding",0.1431,0.1431]
["Net Loss Per Common Share"]
["Total potential dilutive shares",null,2025057,1695494]
["Warrant"]
["Net Loss Per Common Share"]
["Total potential dilutive shares",null,285920,277690]
["Common shares under option"]
["Net Loss Per Common Share"]
["Total potential dilutive shares",null,1729586,1401101]
["Unvested restricted stock"]
["Net Loss Per Common Share"]
["Total potential dilutive shares",null,9551,16703]

{"sheet":"Selected_Quarterly_Financial_D2","index":56,"n_rows":13,"n_cols":12,"rows_kept":13,"cut":false,"hidden":false,"merged":[[0,1,0,8],[0,9,0,11]]}
["Selected Quarterly Financial Data (Unaudited) (USD $)","3 Months Ended",{"$nulls":7},"12 Months Ended"]
["In Thousands, except Share data, unless otherwise specified","Dec. 31, 2014","Sep. 30, 2014","Jun. 30, 2014","Mar. 31, 2014","Dec. 31, 2013","Sep. 30, 2013","Jun. 30, 2013","Mar. 31, 2013","Dec. 31, 2014","Dec. 31, 2013","Dec. 31, 2012"]
["Operating Expenses [Abstract]"]
["Research and development",6200,7174,6528,5400,7338,3483,3100,2093,25302,16014,7998]
["General and administrative",3180,2526,2726,2490,2398,1924,1172,1251,10922,6745,2206]
["Total operating expenses",9380,9700,9254,7890,9736,5407,4272,3344,36224,22759,10204]
["Loss from operations",-9380,-9700,-9254,-7890,-9736,-5407,-4272,-3344,-36224,-22759,-10204]
["Interest expense.",-134,-135,-1,null,null,null,-108,-828,-270,-936,-1486]
["Change in fair value of warrant liability",{"$nulls":6},-2545,-42,null,-2587,32]
["Other income (expense), net",57,29,17,16,46,169,4,-25,119,194,-84]
["Net loss",-9457,-9806,-9238,-7874,-9690,-5238,-6921,-4239,-36375,-26088,-11742]
["Net loss per common share (basic and diluted) (in dollars per share)",-0.49,-0.64,-0.6,-0.51,-0.63,-0.34,-19.82,-12.24,-2.2200000000000002,-3.31,-36.31]
["Weighted-average shares outstanding (basic and diluted) (in shares)",19276639,15432641,15399018,15369055,15340713,15253704,349170,346478,16374102,7885921,323382]

{"sheet":"Uncategorized_Items","index":57,"n_rows":2,"n_cols":2,"rows_kept":2,"cut":false,"hidden":false,"merged":[]}
["Uncategorized Items"]
["[us-gaap_CommonStockSharesIssued]",20352876]