Commitments - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments And Contingencies Disclosure [Abstract]
Rent expenses	$ 3.1	$ 3.0	$ 3.0
Inventory purchase commitments with third-party	$ 1.9	$ 1.2