Goodwill (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020 USD ($)
Goodwill [Roll Forward]
Balance as of December 31, 2019	$ 210,364
Foreign currency translation adjustments	(161)
Balance as of September 30, 2020	210,203
Temporary and consulting staffing
Goodwill [Roll Forward]
Balance as of December 31, 2019	134,210
Foreign currency translation adjustments	(29)
Balance as of September 30, 2020	134,181
Permanent placement staffing
Goodwill [Roll Forward]
Balance as of December 31, 2019	26,097
Foreign currency translation adjustments	(7)
Balance as of September 30, 2020	26,090
Risk consulting and internal audit services
Goodwill [Roll Forward]
Balance as of December 31, 2019	50,057
Foreign currency translation adjustments	(125)
Balance as of September 30, 2020	$ 49,932