Balance Sheet Components - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accrued liabilities
Accrued payroll-related expenses	$ 1,142	$ 1,331
Accrued inventory	183	524
Deferred rent	284	230
Accrued sales commissions payable to sales representatives	92	75
Other	426	94
Total accrued liabilities	$ 2,127	$ 2,254