Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
Net service revenues	$ 1,287,370	$ 1,302,625
Direct costs of services, consisting of payroll, payroll taxes, benefit costs and reimbursable expenses	761,542	770,653
Gross margin	525,828	531,972
Selling, general and administrative expenses	400,249	398,074
Amortization of intangible assets	301	288
Interest income, net	(223)	(181)
Income before income taxes	125,501	133,791
Provision for income taxes	46,980	50,375
Net income	$ 78,521	$ 83,416
Net income per share:
Basic (in usd per share)	$ 0.63	$ 0.65
Diluted (in usd per share)	$ 0.62	$ 0.64
Shares:
Basic (in shares)	125,537	129,281
Diluted (in shares)	126,418	130,137
Cash dividends declared per share (in usd per share)	$ 0.24	$ 0.22