Property and Equipment - Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Major classifications of property and equipment and estimated useful lives
Property and equipment, gross	$ 9,573	$ 9,450
Accumulated depreciation and amortization	(8,529)	(8,062)
Property and equipment, net	1,044	1,388
Office furniture and equipment
Major classifications of property and equipment and estimated useful lives
Property and equipment, gross	4,979	5,041
Leasehold improvements
Major classifications of property and equipment and estimated useful lives
Property and equipment, gross	1,609	1,570
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	$ 2,779	$ 2,633
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 | 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)	10 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