Goodwill (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2021 USD ($)
Goodwill [Roll Forward]
Balance as of December 31, 2020	$ 223,055
Foreign currency translation adjustments	184
Balance as of June 30, 2021	223,239
Temporary and consultant staffing
Goodwill [Roll Forward]
Balance as of December 31, 2020	134,511
Foreign currency translation adjustments	70
Balance as of June 30, 2021	134,581
Permanent placement staffing
Goodwill [Roll Forward]
Balance as of December 31, 2020	26,180
Foreign currency translation adjustments	9
Balance as of June 30, 2021	26,189
Risk consulting and internal audit services
Goodwill [Roll Forward]
Balance as of December 31, 2020	62,364
Foreign currency translation adjustments	105
Balance as of June 30, 2021	$ 62,469