Segment Information (Details) - Reconciliation of Segment Gross Contribution to Net Income - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Costs and expenses:
Cost of services and product development - unallocated		$ 210,495	$ 203,178	$ 388,257	$ 373,999
Selling, general and administrative		237,991	218,537	467,513	423,154
Acquisition and integration charges		3,683	6,644	8,775	10,000
Operating income		85,220	81,761	133,902	140,931
Interest expense and other		5,708	2,505	10,150	4,984
Provision for income taxes		28,357	26,216	44,246	45,171
Net income		51,155	53,040	79,506	90,776
Reportable segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment gross contribution		342,543	318,730	$ 638,377	598,133
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]	5,102	2,088	$ 7,512	5,610
Selling, general and administrative		237,991	218,537	467,513	423,154
Depreciation and amortization		10,547	9,700	20,675	18,438
Acquisition and integration charges		$ 3,683	$ 6,644	$ 8,775	$ 10,000

[1] The unallocated amounts consist of certain bonus and related fringe costs recorded in Consolidated cost of services and product development expense that are not allocated to segment expense. The Company's policy is to only allocate bonus and related fringe charges to segments for up to 100% of the segment employee's target bonus. Amounts above 100% are absorbed by corporate.