Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Beginning balance	$ 209,793	$ 208,579
Acquisitions		1,547
Foreign currency translation adjustments	1,092	(333)
Ending balance	210,885	209,793
Temporary and consultant staffing
Goodwill [Roll Forward]
Beginning balance	133,875	133,173
Acquisitions		1,248
Foreign currency translation adjustments	613	(546)
Ending balance	134,488	133,875
Permanent placement staffing
Goodwill [Roll Forward]
Beginning balance	26,015	26,251
Acquisitions		0
Foreign currency translation adjustments	144	(236)
Ending balance	26,159	26,015
Risk consulting and internal audit services
Goodwill [Roll Forward]
Beginning balance	49,903	49,155
Acquisitions		299
Foreign currency translation adjustments	335	449
Ending balance	$ 50,238	$ 49,903

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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Amount of increase (decrease) from foreign currency translation adjustments and purchase accounting adjustments of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=84229725&loc=d3e961-128460

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