Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Income Statement [Abstract]
Net service revenues	$ 1,302,625	$ 1,205,563
Direct costs of services, consisting of payroll, payroll taxes, benefit costs and reimbursable expenses	770,653	711,476
Gross margin	531,972	494,087
Selling, general and administrative expenses	398,074	365,985
Amortization of intangible assets	288	0
Interest income, net	(181)	(72)
Income before income taxes	133,791	128,174
Provision for income taxes	50,375	50,252
Net income	$ 83,416	$ 77,922
Net income per share:
Basic (in usd per share)	$ 0.65	$ 0.59
Diluted (in usd per share)	$ 0.64	$ 0.58
Shares:
Basic (in shares)	129,281	133,077
Diluted (in shares)	130,137	134,286
Cash dividends declared per share (in usd per share)	$ 0.22	$ 0.20