Business Segments (Business Segments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segment Reporting Information [Line Items]
Net service revenues	$ 973,473	$ 984,668	$ 937,966	$ 880,869	$ 851,572	$ 817,258	$ 769,090	$ 737,173	$ 3,776,976	$ 3,175,093	$ 3,036,547
Operating income (loss)									249,418	115,000	66,780
Amortization of intangible assets									153	411	1,460
Interest income, net									(951)	(579)	(1,443)
Income before income taxes	72,161	72,195	61,284	44,576	43,248	37,268	22,387	12,265	250,216	115,168	66,763
Temporary And Consultant Staffing [Member]
Segment Reporting Information [Line Items]
Net service revenues									3,050,999	2,568,255	2,471,132
Operating income (loss)									209,101	108,443	104,521
Permanent Placement Staffing [Member]
Segment Reporting Information [Line Items]
Net service revenues									302,155	221,219	181,856
Operating income (loss)									35,340	17,502	(6,973)
Risk Consulting And Internal Audit Services [Member]
Segment Reporting Information [Line Items]
Net service revenues									423,822	385,619	383,559
Operating income (loss)									$ 4,977	$ (10,945)	$ (30,768)