Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement [Abstract]
Net service revenues	$ 4,245,895	$ 4,111,213	$ 3,776,976
Direct costs of services, consisting of payroll, payroll taxes, insurance costs and reimbursable expenses	2,522,803	2,462,153	2,287,374
Gross margin	1,723,092	1,649,060	1,489,602
Selling, general and administrative expenses	1,324,815	1,305,614	1,240,184
Amortization of intangible assets	1,700	398	153
Interest income, net	(1,002)	(1,197)	(951)
Income before income taxes	397,579	344,245	250,216
Provision for income taxes	145,384	134,303	100,294
Net income	252,195	209,942	149,922
Net income available to common stockholders-diluted	$ 252,192	$ 208,867	$ 147,772
Net income per share (Note L):
Basic	$ 1.85	$ 1.51	$ 1.05
Diluted	$ 1.83	$ 1.50	$ 1.04
Shares:
Basic	136,153	138,201	140,479
Diluted	137,589	139,409	141,790
Cash dividends declared per share	$ 0.64	$ 0.60	$ 0.56