Selected Balance Sheet Components - Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Property and equipment, net:
Total property and equipment, gross	$ 15,164		$ 15,164		$ 13,411
Finance	166		166		0
Less: Accumulated depreciation	(8,201)		(8,201)		(7,505)
Total, net	6,963		6,963		5,906
Depreciation and amortization	400	$ 400	700	$ 800
Machinery and equipment
Property and equipment, net:
Total property and equipment, gross	2,456		2,456		1,536
Furniture, fixtures and office equipment
Property and equipment, net:
Total property and equipment, gross	775		775		775
Computer equipment and software
Property and equipment, net:
Total property and equipment, gross	5,906		5,906		3,712
Leasehold improvements
Property and equipment, net:
Total property and equipment, gross	4,631		4,631		4,587
Construction in process
Property and equipment, net:
Total property and equipment, gross	$ 1,230		$ 1,230		$ 2,801