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Stockholders' Equity - Reserved Shares of Authorized but Unissued Common Stock (Detail)
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Sep. 30, 2014
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Dec. 31, 2013
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| Class of Stock [Line Items] | ||
| Total reserved shares of common stock | 3,337,333 | 2,320,021 |
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Warrants for common stock [Member]
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| Class of Stock [Line Items] | ||
| Total reserved shares of common stock | 1,787,617 | 1,742,727 |
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Equity incentive plans [Member]
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| Class of Stock [Line Items] | ||
| Total reserved shares of common stock | 1,549,716 | 577,294 |