Segment Information (Details) - Reconciliation of Segment Gross Contribution to Net Income - USD ($) $ in Thousands	3 Months Ended				6 Months Ended	9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2015
Costs and expenses:
Cost of services and product development - unallocated	$ 223,122			$ 193,602		$ 666,585	$ 581,859
Selling, general and administrative	269,902			236,355		799,322	703,868
Acquisition and integration charges	16,557			6,488		32,958	15,263
Operating income	48,726			52,474		196,454	186,376
Interest expense and other, net	3,978			682		14,208	10,832
Provision for income taxes	14,264	$ 25,565	$ 15,320	21,426	$ 40,884	55,149	65,672
Net income	30,484	$ 51,626	$ 44,987	30,366	$ 96,614	127,097	109,872
Reportable segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment gross contribution	355,390			308,103		$ 1,088,960	946,479
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	4,453			1,539		$ 14,222	9,050
Selling, general and administrative	269,902			236,355		799,322	703,868
Depreciation and amortization	15,752			11,247		46,004	31,922
Acquisition and integration charges	$ 16,557			$ 6,488		$ 32,958	$ 15,263