Significant Accounting Policies - Doubtful Accounts (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
After Adoption of ASC 326 [Roll Forward]
Allowance for credit losses, beginning of period	$ 49,179	$ 38,094	$ 49,773	$ 30,931
Additions charged to expense	9,737	11,976	20,559	23,147
Write-offs, net of recoveries	(9,325)	(7,114)	(20,741)	(15,693)
Allowance for credit losses, end of period	49,591	42,956	49,591	42,956
Cumulative Effect Period of Adoption Adjustment
After Adoption of ASC 326 [Roll Forward]
Allowance for credit losses, beginning of period	$ 0	$ 0	$ 0	$ 4,571