Segment Information (Details) - Reconciliation of Segment Gross Contribution to Net Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Costs and expenses:
Cost of services and product development - unallocated	$ 237,609	$ 212,041
Selling, general and administrative	304,244	257,411
Acquisition and integration charges	13,272	8,368
Operating income	53,514	64,429
Interest expense and other, net	5,017	4,122
Provision for income taxes	12,064	15,320
Net income	36,433	44,987
Reportable segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment gross contribution	$ 388,617	350,547
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 - unallocated	$ 1,057	5,322
Selling, general and administrative	304,244	257,411
Depreciation and amortization	16,530	15,017
Acquisition and integration charges	$ 13,272	$ 8,368