Summary of Significant Accounting Policies - Allowance for Sales Credits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	$ 539	$ 367	$ 226
Additions	2,789	1,388	1,845
Deductions	(1,941)	(1,216)	(1,704)
Ending Balance	$ 1,387	$ 539	$ 367