Significant Accounting Policies - Doubtful Accounts (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
After Adoption of ASC 326 [Roll Forward]
Allowance for credit losses, beginning of period	$ 49,773	$ 30,931
Additions charged to expense	10,822	11,171
Write-offs, net of recoveries	(11,416)	(8,579)
Allowance for credit losses, end of period	$ 49,179	38,094
Cumulative Effect Period of Adoption Adjustment
After Adoption of ASC 326 [Roll Forward]
Allowance for credit losses, beginning of period		$ 4,571