Segment Information (Details) - Reconciliation of Segment Gross Contribution to Net Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Costs and expenses:
Cost of services and product development - unallocated	$ 193,602	$ 188,059	$ 581,859	$ 562,058
Selling, general and administrative	236,355	217,025	703,868	640,179
Acquisition and integration charges	6,488	6,015	15,263	16,015
Operating income	52,474	49,391	186,376	190,322
Interest expense and other	682	2,943	10,832	7,927
Provision for income taxes	21,426	12,602	65,672	57,773
Net income	30,366	33,846	109,872	124,622
Reportable segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment gross contribution	308,103	282,833	$ 946,479	880,965
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	1,539	(48)	$ 9,050	5,561
Selling, general and administrative	236,355	217,025	703,868	640,179
Depreciation and amortization	11,247	10,450	31,922	28,888
Acquisition and integration charges	$ 6,488	$ 6,015	$ 15,263	$ 16,015