Quarterly report pursuant to Section 13 or 15(d)

Fair Value of Warrants - Summary of Derivative Warrant Activity (Detail)

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Fair Value of Warrants - Summary of Derivative Warrant Activity (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2017
Mar. 31, 2017
Class of Warrants Outstanding [Roll Forward]    
Fair value of warrants outstanding as of December 31, 2016 $ 2,018  
Fair value of warrants issued 1,004  
Fair value of warrants exercised (2,696)  
Change in fair value of warrants 7,294  
Fair value of warrants outstanding as of March 31, 2017 2,018 $ 7,620
2016 Offering    
Class of Warrants Outstanding [Roll Forward]    
Fair value of warrants outstanding as of December 31, 2016 2,018  
Fair value of warrants issued 0  
Fair value of warrants exercised (2,696)  
Change in fair value of warrants 6,758  
Fair value of warrants outstanding as of March 31, 2017 2,018 6,080
2017 Debt    
Class of Warrants Outstanding [Roll Forward]    
Fair value of warrants outstanding as of December 31, 2016 0  
Fair value of warrants issued 1,004  
Fair value of warrants exercised 0  
Change in fair value of warrants 536  
Fair value of warrants outstanding as of March 31, 2017 $ 0 $ 1,540