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Fair Value Measurements - Additional Information (Detail)
$ in Thousands
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2017
USD ($)
Sep. 30, 2016
USD ($)
Sep. 30, 2017
USD ($)
Input
Sep. 30, 2016
USD ($)
Dec. 31, 2016
USD ($)
Input
Dec. 31, 2015
USD ($)
Fair Value Disclosures [Abstract]            
Number of inputs used for valuation of warrants | Input     6   6  
Derivative warrant liability [Abstract]            
Change in fair value of the warrant liability, net $ (27) $ (8,680) $ (1,227) $ (9,171) $ (12,780) $ (564)
Derivative warrant liabilities $ 16   $ 16   $ 18,751 $ 3,785