Segment Information - Reconciliation of Segment Gross Contribution to Net Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Costs and expenses:
Cost of services and product development	$ 365,056	$ 336,112	$ 1,099,700	$ 1,060,958
Selling, general and administrative	512,159	447,537	1,545,905	1,396,085
Acquisition and integration charges	1,742	17,114	4,156	96,342
Operating income	69,147	52,724	233,948	130,109
Interest expense and other, net	16,049	27,811	66,716	98,454
Gain (loss) from divested operations	0	13,040	(2,075)	38,500
Provision (benefit) for income taxes	11,710	26,200	(432)	31,719
Net income	41,388	11,753	165,589	38,436
Reportable segments
Costs and expenses:
Operating income	636,505	585,304	$ 1,946,370	1,845,286
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	1,059	(258)	$ 4,242	19,669
Selling, general and administrative	512,159	447,537	1,545,905	1,396,085
Depreciation and amortization	52,398	68,187	158,119	203,081
Acquisition and integration charges	1,742	17,114	4,156	96,342
Operating income	$ (567,358)	$ (532,580)	$ (1,712,422)	$ (1,715,177)