Property and Equipment - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 3,447	$ 3,438
Less: accumulated depreciation and amortization	(3,028)	(2,904)
Property and equipment, net	419	534
Machinery and Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,661	1,661
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	243	241
Office Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	230	230
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,312	1,303
Construction in Progress [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1	$ 3

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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