Summary of Significant Accounting Policies - Allowance for Doubtful Accounts Receivable (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for Doubtful Accounts Receivable
Balance, beginning of year	$ 3,735	$ 3,115	$ 4,149
Additions to expense	1,481	778	462
Write-offs	(1,532)	(158)	(1,659)
Other	(56)		163
Balance, end of year	$ 3,628	$ 3,735	$ 3,115