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Stockholders Equity - Additional Information (Detail) - USD ($) | 1 Months Ended | 12 Months Ended
--- | --- | ---
Jan. 31, 2015 | Nov. 30, 2010 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Stockholders Equity Note [Line Items] |  |  |  |  |
Common stock, number of shares issued | 14,636,363 |  |  |  |
Common stock, par value | $ 0.001 |  | $ 0.001 | $ 0.001 |
Public offering, price per share | $ 5.50 |  |  |  |
Estimated Net proceeds from public offering | $ 75,300,000 |  |  |  |
Proceeds from common stock sold |  |  | $ 75,300,000 | $ 18,488,000 | $ 61,425,000
Preferred stock, shares issued |  |  | 0 | 0 |
Stockholder Rights Plan |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |
Minimum percentage of common stock acquired by stockholders |  |  | 15.00% |  |
Designated preferred stock for future issuance |  |  | 250,000 |  |
Series C Junior Participating preferred stock |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |
Preferred stock, shares issued |  |  | 0 |  |
2010 Warrants |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |
Warrants, number of common stock shares |  | 3,700,000 |  |  |
Warrant exercise price |  | $ 3.20 |  |  |
Warrants exercisable date |  | May 15, 2011 |  |  |
Exercisable period |  | 5 years |  |  |
Warrants exercised |  |  | 3,300,000 | 2,600,000 | 200,000
Class of warrants outstanding |  |  | 0 |  |
Cantor | Sales Agreement |  |  |  |  |
Stockholders Equity Note [Line Items] |  |  |  |  |
Common stock, number of shares issued |  |  | 0 | 4,300,000 |
Maximum common stock offering price |  |  | $ 70,000,000 |  |
Percentage of proceeds payable as compensation to underwriter |  |  | 2.00% |  |
Proceeds from common stock sold |  |  | $ 0 | $ 18,600,000 |
Common stock registered for sale |  |  | $ 22,500,000 |  |

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