Property and Equipment - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment	$ 9,234	$ 9,578
Less accumulated depreciation	(6,084)	(5,562)
Property and equipment, net	3,150	4,016
Computer equipment and purchased software
Property, Plant and Equipment [Line Items]
Property and equipment	3,206	3,489
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property and equipment	834	882
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment	1,274	1,290
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment	$ 3,920	$ 3,917