Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Roll Forward]
Beginning balance	$ 209,958	$ 210,885
Foreign currency translation adjustments	406	(927)
Ending balance	210,364	209,958
Temporary and consultant staffing
Goodwill [Roll Forward]
Beginning balance	134,067	134,488
Foreign currency translation adjustments	143	(421)
Ending balance	134,210	134,067
Permanent placement staffing
Goodwill [Roll Forward]
Beginning balance	26,058	26,159
Foreign currency translation adjustments	39	(101)
Ending balance	26,097	26,058
Risk consulting and internal audit services
Goodwill [Roll Forward]
Beginning balance	49,833	50,238
Foreign currency translation adjustments	224	(405)
Ending balance	$ 50,057	$ 49,833