Property and Equipment - Summarized Category of Fixed Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Right of use, building lease	$ 260	$ 471
Total	6,645	6,441
Less accumulated depreciation and amortization	(5,120)	(5,023)
Total property and equipment, net	1,525	1,418
Machinery & equipment
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	4,849	4,683
Computer equipment & software
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	640	272
Office furniture & equipment
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	174	174
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	43	43
Idle equipment
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	679	679
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, gross	$ 0	$ 119