Consolidated Statements of Cash Flows (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Cash flows from operating activities      
Net loss $ (49,963,000) $ (38,759,000) $ (3,415,000)
Adjustments to reconcile net loss to net cash used in operating activities:      
Depreciation and amortization 512,000 489,000 520,000
Amortization of discount and deferred financing costs on notes payable     77,504
Amortization of premiums and accretion of discounts on securities 533,000 651,000 835,000
Share-based compensation expense 2,187,000 2,021,000 1,041,000
Change in fair value of warrant liability (796,000) (2,327,000) (25,520,000)
Cash settled on conversion of restricted share units (96,000) (22,000) (39,000)
Other (1,000) (45,000) 255,000
Net changes in assets and liabilities:      
Accounts and other receivables (101,000) 126,000 11,000
Prepaid and other current assets (168,000) 120,000 (302,000)
Other long-term assets (83,000) 57,000 (307,000)
Accounts payable 144,000 (600,000) 674,000
Accrued and other liabilities (736,000) 1,770,000 (435,000)
Accrued compensation and related liabilities 303,000 269,000 184,000
Deferred rent (102,000) (94,000) (83,000)
Net cash used in operating activities (48,367,000) (36,344,000) (26,503,000)
Cash flows from investing activities      
Purchases of investments (62,411,000) (70,775,000) (72,037,000)
Redemption of investments 71,861,000 68,315,000 64,518,000
Purchases of property and equipment (380,000) (252,000) (752,000)
Cash assumed in connection with the acquisition of Alpine 104,000    
Net cash provided by (used in) investing activities 9,174,000 (2,712,000) (8,271,000)
Cash flows from financing activities      
Proceeds from issuance of common stock and warrants, net of issuance costs 21,668,000 26,069,000 50,466,000
Proceeds from issuance of Series A convertible preferred stock, net of issuance cost 18,693,000    
Proceeds from stock options exercised 7,000   9,000
Principal payment on notes payable     (909,000)
Repayment on notes payable     (4,135,000)
Net cash provided by financing activities 40,368,000 26,069,000 45,431,000
Increase (decrease) in cash and cash equivalents 1,175,000 (12,987,000) 10,657,000
Cash and cash equivalents, beginning of year 9,279,000 22,266,000 11,609,000
Cash and cash equivalents, end of year 10,454,000 9,279,000 22,266,000
Supplemental disclosure of cash flow information      
Interest paid     276,000
Non-cash activities      
Issuance of common stock in connection with the acquisition of Alpine $ 27,233,000