Segment Information - Reconciliation of Segment Gross Contribution to Net Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Costs and expenses:
Cost of services and product development	$ 1,468,800	$ 1,320,198	$ 945,648
Selling, general and administrative	1,884,141	1,599,004	1,089,184
Acquisition and integration charges	107,197	158,450	42,598
Operating income (loss)	259,715	(6,329)	305,141
Interest expense and other, net	124,041	121,488	16,710
Gain from divested operations	45,447	0	0
Provision (benefit) for income taxes	58,665	(131,096)	94,849
Net income	122,456	3,279	193,582
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment gross contribution	2,518,973	2,000,386	1,512,000
Corporate and Reconciling Items
Costs and expenses:
Cost of services and product development	12,319	9,090	13,108
Selling, general and administrative	1,884,141	1,599,004	1,089,184
Depreciation and amortization	255,601	240,171	61,969
Acquisition and integration charges	$ 107,197	$ 158,450	$ 42,598