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Stockholders Equity - Additional Information (Detail) - USD ($) | 1 Months Ended | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | ---
Jan. 31, 2015 | Nov. 30, 2010 | Sep. 30, 2015 | Sep. 30, 2014 | Sep. 30, 2015 | Sep. 30, 2014 | Aug. 31, 2009
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |
Common stock, number of shares issued | 14,636,363 |  |  |  |  |  |
Common stock, par value | $ 0.001 |  |  |  |  |  |
Public offering, price per share | $ 5.50 |  |  |  |  |  |
Estimated Net proceeds from public offering | $ 75,400,000 |  |  |  |  |  |
Underwriting discounts and other issuance costs | $ 5,100,000 |  |  |  |  |  |
(Loss) gain from Revaluation of warrant |  |  | $ 1,100,000 | $ 1,700,000 | $ 4,700,000 | $ 14,300,000 |
2009 Unit Offering |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |
Warrants to purchase an aggregate shares of common stock |  |  |  |  |  |  | 2,400,000
Warrant exercise price |  |  |  |  |  |  | $ 2.90
2010 Unit Offering |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |
Warrants to purchase an aggregate shares of common stock |  | 3,700,000 |  |  |  |  |
Warrant exercise price |  | $ 3.20 |  |  |  |  |
Common stock warrants to purchase outstanding |  |  | 1,800,000 |  | 1,800,000 |  |
2010 Unit Offering | Warrants |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |
Warrants exercisable date |  | May 15, 2011 |  |  |  |  |
Exercisable period |  | 5 years |  |  |  |  |
Common stock issued from the exercise of outstanding warrants |  |  | 175,000 |  | 1,544,123 |  |
Cantor | Sales Agreement |  |  |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |
Common stock, number of shares issued |  |  |  |  | 0 |  |
Maximum common stock offering price |  |  |  |  | $ 70,000,000 |  |
Percentage of proceeds payable as compensation to underwriter |  |  |  |  | 2.00% |  |
Common stock available for sale |  |  | $ 22,500,000 |  | $ 22,500,000 |  |

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