Balance Sheet Information - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 36,771	$ 34,612
Less: Accumulated depreciation and amortization	(25,813)	(24,397)
Land	1,770	1,770
Property and equipment, net	12,728	11,985
Building [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	6,880	6,389
Computers and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	9,966	9,847
Manufacturing and Test Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	15,398	14,192
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	1,440	1,314
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	3,067	2,850
Motor Vehicles [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 20	$ 20