Inventories and Other Deferred Costs - Summary of Inventories and Other Deferred Costs (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw materials	$ 3,830	$ 3,200
Work-in-process	3,907	3,745
Finished products	14,714	12,278
Other deferred costs	1,425	1,823
Total inventory and other deferred costs	$ 23,876	$ 21,046