Property and Equipment - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, Gross	$ 15,717	$ 12,345
Accumulated depreciation and amortization	(8,520)	(6,573)
Property and equipment, net	7,197	5,772
Machinery, Manufacturing and Demonstration Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Gross	10,763	7,579
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Gross	2,137	2,124
Furniture [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Gross	595	614
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Gross	$ 2,222	$ 2,028