Goodwill (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021 USD ($)
Goodwill [Roll Forward]
Balance as of December 31, 2020	$ 223,055
Foreign currency translation adjustments	(163)
Balance as of September 30, 2021	222,892
Temporary and consultant staffing
Goodwill [Roll Forward]
Balance as of December 31, 2020	134,511
Foreign currency translation adjustments	106
Balance as of September 30, 2021	134,617
Permanent placement staffing
Goodwill [Roll Forward]
Balance as of December 31, 2020	26,180
Foreign currency translation adjustments	16
Balance as of September 30, 2021	26,196
Risk consulting and internal audit services
Goodwill [Roll Forward]
Balance as of December 31, 2020	62,364
Foreign currency translation adjustments	(285)
Balance as of September 30, 2021	$ 62,079