The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Sum of operating profit and nonoperating income or expense before Income or Loss from equity method investments, income taxes, extraordinary items, and noncontrolling interest.

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The net amount of operating interest income (expense).

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Business Segments Reconciliation of Revenue and Operating Income by Reportable Segment to Consolidated Results (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Net service revenues	$ 1,221,450us-gaap_SalesRevenueServicesNet	$ 1,224,308us-gaap_SalesRevenueServicesNet	$ 1,164,914us-gaap_SalesRevenueServicesNet	$ 1,084,342us-gaap_SalesRevenueServicesNet	$ 1,083,864us-gaap_SalesRevenueServicesNet	$ 1,075,119us-gaap_SalesRevenueServicesNet	$ 1,063,228us-gaap_SalesRevenueServicesNet	$ 1,023,684us-gaap_SalesRevenueServicesNet	$ 4,695,014us-gaap_SalesRevenueServicesNet	$ 4,245,895us-gaap_SalesRevenueServicesNet	$ 4,111,213us-gaap_SalesRevenueServicesNet
Operating income									497,182us-gaap_OperatingIncomeLoss	398,277us-gaap_OperatingIncomeLoss	343,446us-gaap_OperatingIncomeLoss
Amortization of intangible assets									557us-gaap_AmortizationOfIntangibleAssets	1,700us-gaap_AmortizationOfIntangibleAssets	398us-gaap_AmortizationOfIntangibleAssets
Interest income, net									(724)us-gaap_InterestIncomeExpenseNet	(1,002)us-gaap_InterestIncomeExpenseNet	(1,197)us-gaap_InterestIncomeExpenseNet
Income before income taxes	133,321	138,361	123,653	102,014	103,894	103,713	100,596	89,376	497,349	397,579	344,245
Temporary and consultant staffing
Segment Reporting Information [Line Items]
Net service revenues									3,676,281	3,369,840	3,324,286
Operating income									358,533	301,185	276,826
Permanent placement staffing
Segment Reporting Information [Line Items]
Net service revenues									394,515	347,715	334,198
Operating income									78,333	54,390	55,745
Risk consulting and internal audit services
Segment Reporting Information [Line Items]
Net service revenues									624,218	528,340	452,729
Operating income									$ 60,316	$ 42,702	$ 10,875