Property and Equipment - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 3,031		$ 2,984
Less: accumulated depreciation	(2,641)		(2,595)
Property and equipment, net	390		389
Depreciation	46	$ 105
Equipment
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 1,297		1,297
Equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life	3 years
Equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life	15 years
Tooling
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 203		203
Tooling | Minimum
Property, Plant and Equipment [Line Items]
Useful life	2 years
Tooling | Maximum
Property, Plant and Equipment [Line Items]
Useful life	5 years
Vehicles
Property, Plant and Equipment [Line Items]
Useful life	5 years
Property and equipment at cost	$ 47		47
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Useful life	5 years
Property and equipment at cost	$ 137		137
Computer software
Property, Plant and Equipment [Line Items]
Useful life	3 years
Property and equipment at cost	$ 1,028		1,028
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment at cost	211		211
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	$ 95		$ 48