Goodwill (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Roll Forward]
Beginning balance		$ 210,364	$ 209,958
Foreign currency translation adjustments		492	406
Acquisitions			12,199
Ending balance	$ 223,055	223,055	210,364
Goodwill recorded as a result of acquisition			12,199
Temporary and consultant staffing
Goodwill [Roll Forward]
Beginning balance		134,210	134,067
Foreign currency translation adjustments		301	143
Acquisitions			0
Ending balance	134,511	134,511	134,210
Goodwill recorded as a result of acquisition			0
Permanent placement staffing
Goodwill [Roll Forward]
Beginning balance		26,097	26,058
Foreign currency translation adjustments		83	39
Acquisitions			0
Ending balance	26,180	26,180	26,097
Goodwill recorded as a result of acquisition			0
Risk consulting and internal audit services
Goodwill [Roll Forward]
Beginning balance		50,057	49,833
Foreign currency translation adjustments		108	224
Acquisitions	12,200		12,199
Ending balance	62,364	$ 62,364	50,057
Goodwill recorded as a result of acquisition	$ 12,200		$ 12,199