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Fair Value Measurements and Marketable Securities - Additional Information (Detail) (USD $)
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3 Months Ended | |
|---|---|---|
|
Mar. 31, 2015
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Mar. 31, 2014
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|
| Schedule Of Available For Sale Securities [Line Items] | ||
| Realized gain or losses | $ 0 | $ 0 |
| Weighted average maturity for available for sale securities | 4 months 27 days | |
| February 2015 and March 2011 Offering | ||
| Schedule Of Available For Sale Securities [Line Items] | ||
| Shares of common stock to be purchased with warrants | 12,100,000 | |
| Maximum | ||
| Schedule Of Available For Sale Securities [Line Items] | ||
| Available for sale securities, longest maturity date | 2016-05 | |