Segment Information Segment Information (Detail) - Reconciliation of Segment Gross Contribution to Net Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Costs and expenses:
Cost of services and product development	$ 839,076	$ 797,933	$ 713,484
Selling, general and administrative	962,677	876,067	760,458
Acquisition and integration charges	26,175	21,867	337
Operating income	287,997	286,162	275,492
Interest expense and other	15,786	11,479	9,053
Provision for income taxes	96,576	90,917	83,638
Net income	175,635	183,766	182,801
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment gross contribution	1,334,547	1,234,229	1,078,165
Corporate and Reconciling Items
Costs and expenses:
Cost of services and product development	10,567	10,721	7,436
Selling, general and administrative	962,677	876,067	760,458
Depreciation and amortization	47,131	39,412	34,442
Acquisition and integration charges	$ 26,175	$ 21,867	$ 337