Summary of Significant Accounting Policies - Allowance for doubtful accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies
Balance at Beginning of Period	$ 469	$ 648	$ 671	$ 759
Charged to Costs and Expenses	56	420	578
Write Off of Uncollectible Accounts, Net of Recoveries	(235)	(443)	(666)
Balance at End of Period	$ 469	$ 648	$ 671	$ 759