Revenue and Related Matters - Schedule of Contract with Customer, Asset and Liability (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Assets:
Fees receivable, gross	$ 958,864		$ 958,864		$ 1,334,012
Contract assets recorded in Prepaid expenses and other current assets	23,990		23,990		21,350
Contract liabilities:
Deferred revenues (current liability)	1,710,791		1,710,791		1,928,020
Non-current deferred revenues recorded in Other liabilities	26,051		26,051		24,409
Total contract liabilities	1,736,842		1,736,842		$ 1,952,429
Revenue recognized previously attributable to deferred revenues	$ 681,600	$ 675,200	$ 1,354,200	$ 1,312,300