Property and Equipment - Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Major classifications of property and equipment and estimated useful lives
Property and equipment, gross	$ 10,072	$ 9,868
Accumulated depreciation and amortization	(9,328)	(8,962)
Property and equipment, net	744	906
Office furniture and equipment
Major classifications of property and equipment and estimated useful lives
Property and equipment, gross	5,410	5,219
Leasehold improvements
Major classifications of property and equipment and estimated useful lives
Property and equipment, gross	1,610	1,610
Vehicles
Major classifications of property and equipment and estimated useful lives
Property and equipment, gross	206	206
Manufacturing and test equipment
Major classifications of property and equipment and estimated useful lives
Property and equipment, gross	$ 2,846	$ 2,833
Minimum
Major classifications of property and equipment and estimated useful lives
Property and equipment, useful life (in years)	2 years
Minimum | Office furniture and equipment
Major classifications of property and equipment and estimated useful lives
Property and equipment, useful life (in years)	3 years
Minimum | Leasehold improvements
Major classifications of property and equipment and estimated useful lives
Property and equipment, useful life (in years)	2 years
Minimum | Vehicles
Major classifications of property and equipment and estimated useful lives
Property and equipment, useful life (in years)	5 years
Minimum | Manufacturing and test equipment
Major classifications of property and equipment and estimated useful lives
Property and equipment, useful life (in years)	2 years
Maximum
Major classifications of property and equipment and estimated useful lives
Property and equipment, useful life (in years)	10 years
Maximum | Office furniture and equipment
Major classifications of property and equipment and estimated useful lives
Property and equipment, useful life (in years)	10 years
Maximum | Leasehold improvements
Major classifications of property and equipment and estimated useful lives
Property and equipment, useful life (in years)	7 years
Maximum | Vehicles
Major classifications of property and equipment and estimated useful lives
Property and equipment, useful life (in years)	10 years
Maximum | Manufacturing and test equipment
Major classifications of property and equipment and estimated useful lives
Property and equipment, useful life (in years)	10 years