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Inventories - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Inventory Disclosure [Abstract]        
Amounts credited to the allowance for obsolete inventory $ 0.5 $ 0.1 $ 0.8 $ 1.0