Inventory (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Inventory, finished goods, trial and evaluation, gross	$ 1,700	$ 1,400
Raw materials	20,288	20,119
Finished goods	23,679	25,346
Total inventory	$ 43,967	$ 45,465