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, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Equity [Abstract]        
Beginning Balance     $ 32,558  
Change in fair value of common stock warrants 5,822 (19,852) 8,938 88,539
Exercise of warrants     (7,513)  
Ending Balance $ 33,983   $ 33,983