Inventory (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Inventory, finished goods, trial and evaluation, gross	$ 1,300	$ 1,400
Raw materials	20,574	19,670
Finished goods	17,013	14,093
Total inventory	$ 37,587	$ 33,763