Segment Information - Reconciliation of Segment Gross Contribution to Net Income (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Costs and expenses:
Cost of services and product development	$ 329,767			$ 365,056			$ 993,596	$ 1,099,700
Selling, general and administrative	521,508			512,159			1,512,987	1,545,905
Acquisition and integration charges	1,722			1,742			5,438	4,156
Operating income	87,650			69,147			312,020	233,948
Interest expense and other, net	(28,669)			(16,049)			(97,228)	(66,716)
Loss from divested operations	0			0			0	(2,075)
Loss on extinguishment of debt	(44,814)			0			(44,814)	0
Less: (Benefit) provision for income taxes	(2,797)			11,710			22,840	(432)
Net income	16,964	$ 55,077	$ 75,097	41,388	$ 103,406	$ 20,795	147,138	165,589
Reportable segments
Costs and expenses:
Operating income	672,533			636,505			$ 2,004,262	1,946,370
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	7,682			1,059			$ 11,214	4,242
Selling, general and administrative	521,508			512,159			1,512,987	1,545,905
Depreciation and amortization	53,971			52,398			162,603	158,119
Acquisition and integration charges	1,722			1,742			5,438	4,156
Operating income	$ (584,883)			$ (567,358)			$ (1,692,242)	$ (1,712,422)