Property and Equipment - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 15,674	$ 17,499
Accumulated depreciation and amortization	(10,968)	(11,162)
Property and equipment, net	4,706	6,337
Machinery, Manufacturing and Demonstration Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	10,421	12,320
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,321	2,260
Furniture
Property, Plant and Equipment [Line Items]
Property and equipment, gross	637	639
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,295	$ 2,280