Balance Sheet Components - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accrued liabilities
Accrued payroll-related expenses	$ 1,485	$ 1,331
Accrued joint development agreement expenses	4,711	749
Accrued inventory	1,038	897
Deferred rent	382	230
Accrued sales commissions payable to sales representatives	104	75
Other	868	466
Total accrued liabilities	$ 8,588	$ 3,748