Segment Information (Details) - Reconciliation of Segment Gross Contribution to Net Income (USD $) In Thousands, unless otherwise specified	3 Months Ended				12 Months Ended	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Reportable segments	Mar. 31, 2013 Reportable segments	Dec. 31, 2013 Reportable segments Maximum	Mar. 31, 2014 Unallocated amount to segments		Mar. 31, 2013 Unallocated amount to segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment gross contribution	$ 279,402	$ 244,860	$ 279,402	$ 244,860
Costs and expenses:
Cost of services and product development - unallocated						3,521	[1]	1,843	[1]
Selling, general and administrative	204,617	180,478	204,617	180,478
Depreciation and amortization			8,738	8,434
Acquisition and integration charges	3,356	100	3,356	100
Operating income	59,170	54,005	59,170	54,005
Interest expense and other			2,479	2,225
Provision for income taxes	18,955	15,105	18,955	15,105
Net income	$ 37,736	$ 36,675	$ 37,736	$ 36,675
Percent of target bonus allocated to segments					100.00%

[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.