Segment Information (Details) - Reconciliation of Segment Gross Contribution to Net Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment gross contribution	$ 295,834		$ 279,402
Costs and expenses:
Selling, general and administrative	229,522		204,617
Acquisition and integration charges	5,092		3,356
Operating income	48,682		59,170
Provision for income taxes	15,889		18,955
Net income	28,351		37,736
Reportable segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment gross contribution	295,834		279,402
Costs and expenses:
Selling, general and administrative	229,522		204,617
Depreciation and amortization	10,128		8,738
Acquisition and integration charges	5,092		3,356
Operating income	48,682		59,170
Interest expense and other	4,442		2,479
Provision for income taxes	15,889		18,955
Net income	28,351		37,736
Reportable segments | Maximum
Costs and expenses:
Percent of target bonus allocated to segments	100.00%
Unallocated amount to segments
Costs and expenses:
Cost of services and product development - unallocated	$ 2,410	[1]	$ 3,521	[1]

[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.