Balance Sheets Details - Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Balance Sheets Details [Abstract]
Accrued purchases	$ 1,084	$ 941
Accrued professional and outside service fees	1,728	2,393
Accrued expenses - cost of sales	1,318	0
Deferred rent	278	258
Lease incentive obligation	425	425
Other	471	345
Total	$ 5,304	$ 4,362