Balance Sheet Information - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 33,802	$ 33,754
Less: Accumulated depreciation and amortization	(23,832)	(23,386)
Land	1,770	1,770
Property and equipment, net	11,740	12,138
Building [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	6,372	6,351
Computers and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	10,649	10,963
Manufacturing and Test Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	13,886	13,573
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	1,319	1,318
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	1,556	1,529
Motor Vehicles [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 20	$ 20