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Fair Value of Financial Instruments - Summary of Change in Fair Value of Level 3 Financial Instruments (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Fair Value Disclosures [Abstract]    
Balance, beginning of year $ 1,107 $ 1,767
Change in fair value of derivative liability (635) (660)
Gain on the extinguishment of derivative liability $ (472)  
Balance, end of year   $ 1,107