Property and Equipment Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 13,272	$ 12,975
Accumulated depreciation and amortization	(10,287)	(9,426)
Total property and equipment, net	2,985	3,549
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	5,678	5,678
Machinery and equipment
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	1,925	1,603
Demonstration equipment
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	167	145
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	871	794
Computer equipment
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	603	591
Computer software
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	2,908	2,935
Consigned equipment
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	1,058	1,010
Construction-in-progress
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 62	$ 219