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 6 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Jun. 30, 2013
Class Of Warrant Or Right [Line Items]        
Beginning Balance     $ 23,421  
Change in fair value of common stock warrants (6,665) 5,822 (8,122) 8,938
Exercise of warrants         
Ending Balance $ 15,299   $ 15,299