Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Reconciliation of Warrant Liability Measured at Fair Value (Detail)

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Stockholders' Equity - Reconciliation of Warrant Liability Measured at Fair Value (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2014
Mar. 31, 2013
Equity [Abstract]    
Beginning Balance $ 23,421  
Change in fair value of common stock warrants (1,457) 3,116
Exercise of warrants     
Ending Balance $ 21,964