Significant Balance Sheet Components - Prepaid Royalties and Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accrued commissions	$ 4,567	$ 4,398
Accrued stock-settled bonus	5,454	9,355
Employee Stock Purchase Plan liability	890	1,923
Other accrued payroll-related expenses	3,113	3,630
Accrued royalties	2,091	3,596
Other accrued liabilities	4,337	4,445
Total accrued expenses	20,452	27,347
Prepaid expenses and other current assets
Prepaid royalties	7,800	3,800
Other assets
Prepaid royalties	$ 3,300	$ 3,400