Inventory (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Inventory, finished goods, trial and evaluation hardware	$ 1,400	$ 1,400
Raw materials	19,670	20,119
Finished goods	14,093	25,346
Total inventory	$ 33,763	$ 45,465