Balance Sheets Details - Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Balance Sheets Details [Abstract]
Accrued purchases	$ 834	$ 941
Accrued professional and outside service fees	1,666	2,393
Accrued expenses - cost of sales	1,387	0
Deferred rent	297	258
Lease incentive obligation	425	425
Other	442	345
Total	$ 5,051	$ 4,362