Significant Accounting Policies - Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Prior to Adoption of ASC 326 [Roll Forward]
Allowance for credit losses, beginning of period	$ 30,931	$ 28,457	$ 12,687
Additions charged to expense		49,072	37,704
Additions from merger		2,207	6,601
Write-offs, net of recoveries		(48,805)	(28,535)
Allowance for credit losses, end of period		30,931	$ 28,457
After Adoption of ASC 326 [Roll Forward]
Allowance for credit losses, beginning of period	30,931
Additions charged to expense	49,130
Additions from merger	3,503
Write-offs, net of recoveries	(38,362)
Allowance for credit losses, end of period	49,773	30,931
Cumulative Effect, Period of Adoption, Adjustment
After Adoption of ASC 326 [Roll Forward]
Allowance for credit losses, beginning of period	$ 4,571
Allowance for credit losses, end of period		$ 4,571