Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued payroll and related expenses	$ 5,642	$ 9,151
Provisions for sales returns	2,735	2,419
Accrued professional services	380	682
Operating lease liability	788	769
Accrued royalty expense	477	470
Deferred revenue	174	304
Accrued travel expenses	276	431
Accrued clinical expenses	181	241
Accrued other expenses	472	567
Total	$ 11,125	$ 15,034