Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement [Abstract]
Net service revenues	$ 1,312,718	$ 1,224,308	$ 3,790,339	$ 3,473,564
Direct costs of services, consisting of payroll, payroll taxes, benefit costs and reimbursable expenses	762,917	719,088	2,215,949	2,051,405
Gross margin	549,801	505,220	1,574,390	1,422,159
Selling, general and administrative expenses	390,735	366,967	1,138,075	1,058,144
Amortization of intangible assets	0	0	0	557
Interest income, net	(240)	(108)	(400)	(570)
Income before income taxes	159,306	138,361	436,715	364,028
Provision for income taxes	62,581	53,177	172,362	142,153
Net income	$ 96,725	$ 85,184	$ 264,353	$ 221,875
Net income per share:
Basic (in usd per share)	$ 0.74	$ 0.64	$ 2.00	$ 1.65
Diluted (in usd per share)	$ 0.73	$ 0.63	$ 1.98	$ 1.63
Shares:
Basic (in shares)	131,285	134,054	132,280	134,690
Diluted (in shares)	132,488	135,366	133,436	135,740
Cash dividends declared per share	$ 0.20	$ 0.18	$ 0.60	$ 0.54