Inventories - Changes in Inventory Reserve (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Inventory Disclosure [Abstract]
Beginning balance	$ (4,672)	$ (7,966)	$ (6,391)	$ (7,177)
Inventory reserve charged to costs of sales	(1,504)	(1,399)	(2,515)	(2,286)
Sale of previously reserved inventory	898	2,943	1,118	3,445
Change in reserve	(606)	1,544	(1,397)	1,159
Write off	339	983	2,863	1,150
Translation adjustments	240	142	226	(429)
Ending balance	$ (4,699)	$ (5,297)	$ (4,699)	$ (5,297)