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Shareholders' Equity - Additional Information (Details) (USD $)
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3 Months Ended |
1 Months Ended |
12 Months Ended |
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Mar. 31, 2015
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Jan. 31, 2015
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Dec. 31, 2014
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Mar. 31, 2013
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Oct. 31, 2014
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| Shareholders' Equity (Deficit) (Textual) [Abstract] |
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| Issuance of common shares upon exercise of options, shares |
74,902 |
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| Weighted average exercise price of common stock |
$ 7.33 |
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| Common stock sale value |
$ 43,588 |
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$ 37,475 |
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| Proceeds from issuance of common stock, net of underwriting discounts |
139,043,625 |
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| Cowen And Company Limited Liability Company | At The Market Sales Agreement |
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| Shareholders' Equity (Deficit) (Textual) [Abstract] |
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| Common stock sale value |
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25,000,000 |
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| Commission on sale of common stock under the ATM |
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3.00% |
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| Cowen And Company Limited Liability Company | Amended And Restated Agreement |
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| Shareholders' Equity (Deficit) (Textual) [Abstract] |
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| Common stock sale value |
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50,000,000 |
| Common Stock |
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| Shareholders' Equity (Deficit) (Textual) [Abstract] |
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| Number of common stocks issued through public offering |
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6,037,500 |
4,092,525 |
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| Common share price |
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$ 24.50 |
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| Proceeds from issuance of common stock, net of underwriting discounts and offering costs |
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138,800,000 |
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| Underwriting discounts, commissions and expenses |
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9,100,000 |
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| Issuance of common shares upon exercise of options, shares |
74,902 |
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| Weighted average exercise price of common stock |
$ 7.33 |
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| Proceeds from issuance of common stock, net of underwriting discounts |
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48,500,000 |
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| Commissions |
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$ 1,500,000 |
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