Summary of Significant Accounting Policies - Account Receivable (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts Receivable, Allowance for Credit Loss
Balance, beginning of year	$ 5,230	$ 5,545	$ 5,378
Provision for losses	3,929	4,154	4,181
Write-offs	(2,573)	(4,469)	(4,014)
Balance, end of year	$ 6,586	$ 5,230	$ 5,545