Segment Information (Details) - Reconciliation of Segment Gross Contribution to Net Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Costs and expenses:
Cost of services and product development	$ 1,320,198	$ 945,648	$ 839,076
Selling, general and administrative	1,599,004	1,089,184	962,677
Acquisition and integration charges	158,450	42,598	26,175
Operating (loss) income	(6,329)	305,141	287,997
Interest expense and other, net	121,488	16,710	15,786
(Benefit) provision for income taxes	(131,096)	94,849	96,576
Net income	3,279	193,582	175,635
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment gross contribution	2,000,386	1,512,000	1,334,547
Corporate and Reconciling Items
Costs and expenses:
Cost of services and product development	9,090	13,108	10,567
Selling, general and administrative	1,599,004	1,089,184	962,677
Depreciation and amortization	240,171	61,969	47,131
Acquisition and integration charges	$ 158,450	$ 42,598	$ 26,175