Summary of Significant Accounting Policies - Credit Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies
Beginning balance	$ 2,919	$ 1,788	$ 2,000
Cumulative-effect adjustment upon adoption of ASU 2016-13	404	200
Provision for credit losses	1,354	1,141	(41)
Write-offs	(457)	(10)	(171)
Ending balance	$ 4,220	$ 2,919	$ 1,788