Balance Sheet Components - Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Accrued sales commission payable	$ 273	$ 310
Accrued manufacturing expenses	310	265
Deferred rent, current portion	431	422
Liabilities to certain customers	732	468
Other accrued liabilities	760	894
Total accrued expenses and other current liabilities	$ 2,506	$ 2,359