Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued payroll and related expenses	$ 9,573	$ 9,151
Provision for sales returns	820	2,419
Accrued professional services	2,520	682
Recall replacement obligation	1,696	0
Operating lease liability	850	769
Accrued royalty expense	518	470
Deferred revenue	206	304
Accrued travel expenses	237	431
Accrued clinical expenses	113	241
Accrued other expenses	424	567
Accrued liabilities	$ 16,957	$ 15,034	$ 721