Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 3,193		$ 3,084
Less: accumulated depreciation	(2,711)		(2,664)
Property and equipment, net	482		420
Depreciation	47	$ 46
Equipment
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 1,281		1,281
Equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life (in years)	3 years
Equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life (in years)	15 years
Tooling
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 240		240
Tooling | Minimum
Property, Plant and Equipment [Line Items]
Useful life (in years)	2 years
Tooling | Maximum
Property, Plant and Equipment [Line Items]
Useful life (in years)	5 years
Vehicles
Property, Plant and Equipment [Line Items]
Useful life (in years)	5 years
Property and equipment at cost	$ 80		47
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Useful life (in years)	5 years
Property and equipment at cost	$ 137		137
Computer software
Property, Plant and Equipment [Line Items]
Useful life (in years)	3 years
Property and equipment at cost	$ 1,121		1,057
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment at cost	169		169
Finance lease right-of-use asset
Property, Plant and Equipment [Line Items]
Property and equipment at cost	13		13
Projects in progress
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 152		$ 140