Balance Sheet Components - Property and Equipment Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property and Equipment, Net
Total property and equipment, gross	$ 13,322	$ 10,105
Less: accumulated depreciation	(9,376)	(8,185)
Total property and equipment, net	3,946	1,920
Depreciation and amortization expense	1,200	700	$ 1,200
Manufacturing equipment
Property and Equipment, Net
Total property and equipment, gross	10,465	8,983
Computer and network equipment
Property and Equipment, Net
Total property and equipment, gross	710	588
Furniture and fixtures
Property and Equipment, Net
Total property and equipment, gross	218	188
Software
Property and Equipment, Net
Total property and equipment, gross	455	333
Leasehold improvements
Property and Equipment, Net
Total property and equipment, gross	$ 1,474	$ 13