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Stockholders Equity - Additional Information (Detail) (USD $) | 3 Months Ended |  | 3 Months Ended |  | 3 Months Ended |  |  | 1 Months Ended | 12 Months Ended | 3 Months Ended |  | 3 Months Ended | 12 Months Ended
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Mar. 31, 2014 | Mar. 31, 2013 | Dec. 31, 2013 | Mar. 31, 2013 IPO | Mar. 19, 2013 IPO | Mar. 31, 2013 IPO Overallotment Option | Aug. 31, 2009 2009 Unit Offering | Nov. 30, 2010 2010 Unit Offering | Aug. 31, 2009 Warrant 2009 Unit Offering | Nov. 30, 2010 Warrant 2010 Unit Offering | Dec. 31, 2013 Warrant 2010 Unit Offering | Mar. 31, 2014 Stockholder Rights Plan | Mar. 31, 2014 Sales Agreement Mlv | Mar. 31, 2014 Sales Agreement Mlv Maximum | Mar. 31, 2014 Sales Agreement Cantor | Dec. 31, 2013 Sales Agreement Cantor
Stockholders Equity Note [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Warrants to purchase an aggregate shares of common stock |  |  |  |  |  |  |  | 2,400,000 | 3,700,000 |  |  |  |  |  |  |  |
Warrant exercise price |  |  |  |  |  |  |  | 2.90 | 3.20 |  |  |  |  |  |  |  |
Exercisable period |  |  |  |  |  |  |  |  |  | 5 years | 5 years |  |  |  |  |  |
Warrant liability | $ 11,356,000 |  | $ 20,390,000 | [1] |  |  |  |  |  | $ 2,800,000 | $ 5,800,000 |  |  |  |  |  |
Risk-free interest rate |  |  |  |  |  |  |  |  |  | 2.48% | 1.23% |  |  |  |  |  |
Expected term (in years) |  |  |  |  |  |  |  |  |  | 5 years | 5 years |  |  |  |  |  |
Expected dividend yield |  |  |  |  |  |  |  |  |  | 0.00% | 0.00% |  |  |  |  |  |
Estimated volatility |  |  |  |  |  |  |  |  |  | 77.00% | 85.00% |  |  |  |  |  |
Net proceeds from underwritten public offering |  |  |  |  |  |  |  |  |  |  | 19,700,000 |  |  |  |  |  |
Payment for underwriting discounts and commissions and stock issuance cost |  |  |  |  | 500,000 |  |  |  |  |  | 1,300,000 |  |  |  |  |  |
Number of units sold in underwritten public offering |  |  |  |  |  |  |  |  |  |  | 7,400,000 |  |  |  |  |  |
Number of common stock in each unit |  |  |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |
Number of common stock shares purchasable with each warrant |  |  |  |  |  |  |  |  |  |  | 0.5 |  |  |  |  |  |
Units issued, price per unit |  |  |  |  |  |  |  |  |  |  | $ 2.85 |  |  |  |  |  |
Common stock, number of shares issued |  |  |  |  | 8,300,000 |  | 1,300,000 |  |  |  | 7,400,000 |  |  |  |  | 0 | 5,400,000
Warrants exercisable date |  |  |  |  |  |  |  |  |  |  | May 15, 2011 |  |  |  |  |  |
Gain (loss) from revaluation of warrant liability | 9,034,000 | (5,073,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Warrants exercised |  |  |  |  |  |  |  |  |  |  |  | 186,586 |  |  |  |  |
Maximum common stock offering price |  |  |  |  |  |  |  |  |  |  |  |  |  | 20,000,000 |  | 70,000,000 |
Common stock available for sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100,000 | 41,500,000 |
Percentage of proceeds payable as compensation to underwriter |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.00% |
Proceeds from common stock sold | 31,000 | 51,502,000 |  |  | 38,000,000 |  |  |  |  |  |  |  |  |  |  | 0 | 23,500,000
Common stock, price per share |  |  |  |  |  | $ 4.20 |  |  |  |  |  |  |  |  |  |  |
Gross proceeds from public offering |  |  |  |  | 40,300,000 |  |  |  |  |  |  |  |  |  |  |  |
Underwriter's discount |  |  |  |  | $ 1,800,000 |  |  |  |  |  |  |  |  |  |  |  |
Minimum percentage of common stock acquired by stockholders |  |  |  |  |  |  |  |  |  |  |  |  | 15.00% |  |  |  |
Designated preferred stock for future issuance |  |  |  |  |  |  |  |  |  |  |  |  | 250,000 |  |  |  |
[1] | The financial information in this column was derived from audited financial statements included in the Company's 2013 Annual Report on Form 10-K.

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