Segment Information - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Revenue	$ 608,351	$ 535,177	$ 1,210,812	$ 1,067,618
Nurse and Allied Solutions
Segment Reporting Information [Line Items]
Revenue	444,464	367,994	868,810	741,466
Physician and Leadership Solutions
Segment Reporting Information [Line Items]
Revenue	108,622	142,449	246,464	279,526
Technology and Workforce Solutions
Segment Reporting Information [Line Items]
Revenue	55,265	24,734	95,538	46,626
Temporary staffing
Segment Reporting Information [Line Items]
Revenue	541,195	490,165	1,085,137	982,477
Temporary staffing | Nurse and Allied Solutions
Segment Reporting Information [Line Items]
Revenue	444,464	367,994	868,810	741,466
Temporary staffing | Physician and Leadership Solutions
Segment Reporting Information [Line Items]
Revenue	95,701	122,171	215,297	241,011
Temporary staffing | Technology and Workforce Solutions
Segment Reporting Information [Line Items]
Revenue	1,030	0	1,030	0
Permanent placement
Segment Reporting Information [Line Items]
Revenue	12,921	20,278	31,167	38,515
Permanent placement | Nurse and Allied Solutions
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Permanent placement | Physician and Leadership Solutions
Segment Reporting Information [Line Items]
Revenue	12,921	20,278	31,167	38,515
Permanent placement | Technology and Workforce Solutions
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Outsourced workforce
Segment Reporting Information [Line Items]
Revenue	30,836	4,097	48,516	7,792
Outsourced workforce | Nurse and Allied Solutions
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Outsourced workforce | Physician and Leadership Solutions
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
Outsourced workforce | Technology and Workforce Solutions
Segment Reporting Information [Line Items]
Revenue	30,836	4,097	48,516	7,792
SaaS-based technologies
Segment Reporting Information [Line Items]
Revenue	23,399	20,637	45,992	38,834
SaaS-based technologies | Nurse and Allied Solutions
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
SaaS-based technologies | Physician and Leadership Solutions
Segment Reporting Information [Line Items]
Revenue	0	0	0	0
SaaS-based technologies | Technology and Workforce Solutions
Segment Reporting Information [Line Items]
Revenue	$ 23,399	$ 20,637	$ 45,992	$ 38,834