Segment Information - Reconciliation of Segment Gross Contribution to Net Income (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended						9 Months Ended
	May 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Costs and expenses:
Cost of services and product development		$ 359,237			$ 329,767			$ 1,044,506	$ 993,596
Selling, general and administrative		512,573			521,508			1,488,324	1,512,987
Acquisition and integration charges		1,771			1,722			3,713	5,438
Operating income		230,221			87,650			730,347	312,020
Interest expense and other, net		(31,388)			(28,669)			(73,119)	(97,228)
Gain on event cancellation insurance claims	$ 135,500	0			0			135,545	0
Loss on extinguishment of debt		0			(44,814)			0	(44,814)
Less: Provision (benefit) for income taxes		49,968			(2,797)			208,572	22,840
Net income		148,865	$ 271,236	$ 164,100	16,964	$ 55,077	$ 75,097	584,201	147,138
Reportable segments
Costs and expenses:
Operating income		811,519			672,533			$ 2,416,388	2,004,262
Reportable segments | Maximum
Costs and expenses:
Percent of target bonus allocated to segments								100.00%
Corporate and other expenses
Costs and expenses:
Cost of services and product development		14,474			7,682			$ 33,255	11,214
Selling, general and administrative		512,573			521,508			1,488,324	1,512,987
Depreciation and amortization		52,480			53,971			160,749	162,603
Acquisition and integration charges		1,771			1,722			3,713	5,438
Operating income		$ (581,298)			$ (584,883)			$ (1,686,041)	$ (1,692,242)