Summary of Significant Accounting Policies - Allowance for doubtful accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Summary of Significant Accounting Policies
Balance at Beginning of Period	$ 648	$ 671	$ 759	$ 727
Charged to Costs and Expenses	420	578	444
Allowance From Acquisitions			25
Write Off of Uncollectible Accounts, Net of Recoveries	(443)	(666)	(437)
Balance at End of Period	$ 648	$ 671	$ 759	$ 727