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Property and Equipment, net - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Property Plant And Equipment [Abstract]        
Depreciation expense $ 0.8 $ 0.2 $ 2.2 $ 0.5