Balance Sheet Components (PPE) (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, gross	$ 6,804	$ 4,178
Less accumulated depreciation	(2,041)	(1,192)
Property and equipment, net	4,763	2,986
Depreciation expense	900	400	$ 300
Leasehold improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	402	86
Manufacturing equipment and toolings
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,260	2,264
Computer equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	387	287
Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	797	669
Office equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	142	129
Furniture and fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 816	$ 743