Contract Balances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at Beginning of Period	$ 19,280	$ 16,956	$ 15,056
Current Period Provision For Expected Credit Losses	76,441	69,866	98,461
Write-offs Charged Against Allowance	(52,488)	(67,542)	(96,561)
Balance at End of Period	43,233	19,280	$ 16,956
Balance at Beginning of Period	609,054
Recognition of unearned revenue	(5,852,961)
Deferral of revenue	5,837,704
Balance at End of Period	$ 593,797	$ 609,054
Remaining performance obligations	true