Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 3,411	$ 4,690
Less: accumulated depreciation	(2,314)	(2,365)
Property and equipment, net	1,097	2,325
Depreciation	681	805	$ 266
Impairment loss on equipment and software	$ 185	857
Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	15 years
Equipment
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 1,557	$ 2,231
Equipment | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years	3 years
Equipment | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	15 years	15 years
Tooling
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 371	$ 863
Tooling | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years	2 years
Tooling | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years	5 years
Vehicles
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 47	$ 39
Property and equipment, useful life	5 years	5 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 137	$ 170
Property and equipment, useful life	5 years	5 years
Computer software
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 1,043	$ 977
Property and equipment, useful life	3 years	3 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 201	$ 256
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment at cost	$ 55	$ 154