Business Segments Reconciliation of Revenue and Operating Income by Reportable Segment (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Net service revenues	$ 1,205,563us-gaap_SalesRevenueServicesNet	$ 1,084,342us-gaap_SalesRevenueServicesNet
Operating income	128,102us-gaap_OperatingIncomeLoss	102,109us-gaap_OperatingIncomeLoss
Amortization of intangible assets	0us-gaap_AmortizationOfIntangibleAssets	333us-gaap_AmortizationOfIntangibleAssets
Interest income, net	(72)us-gaap_InterestIncomeExpenseNet	(238)us-gaap_InterestIncomeExpenseNet
Income before income taxes	128,174	102,014
Temporary and consultant staffing
Segment Reporting Information [Line Items]
Net service revenues	943,518	857,570
Operating income	92,801	77,485
Permanent placement staffing
Segment Reporting Information [Line Items]
Net service revenues	98,413	92,625
Operating income	19,031	17,275
Risk consulting and internal audit services
Segment Reporting Information [Line Items]
Net service revenues	163,632	134,147
Operating income	$ 16,270	$ 7,349

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

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-Section 45

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-Name Accounting Standards Codification

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-Section 50

-Paragraph 2

-Subparagraph (a)(2)

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+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
Period Type:	duration

- Definition

This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses from ongoing operations, after income or loss from equity method investments, but before income taxes, extraordinary items, and noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 940

-SubTopic 20

-Section 25

-Paragraph 1

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-Name Accounting Standards Codification

-Topic 235

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-Section S99

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 10

-Article 5

+ Details

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- Definition

The net amount of operating interest income (expense).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.10)

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- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

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- Definition

Aggregate revenue during the period from services rendered in the normal course of business, after deducting allowances and discounts.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

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-Paragraph 2

-Subparagraph (SX 210.5-03.1(d))

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