CUSTOMER CONTRACTS - 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
Disaggregation of Revenue [Line Items]
Revenue	$ 216,779	$ 202,757	$ 426,843	$ 397,928
Temporary Staffing Services
Disaggregation of Revenue [Line Items]
Revenue	209,412	194,560	411,520	382,377
Other Services
Disaggregation of Revenue [Line Items]
Revenue	7,367	8,197	15,323	15,551
Nurse And Allied Staffing
Disaggregation of Revenue [Line Items]
Revenue	198,098	180,787	386,331	356,424
Nurse And Allied Staffing | Temporary Staffing Services
Disaggregation of Revenue [Line Items]
Revenue	193,331	177,733	378,279	350,396
Nurse And Allied Staffing | Other Services
Disaggregation of Revenue [Line Items]
Revenue	4,767	3,054	8,052	6,028
Physician Staffing
Disaggregation of Revenue [Line Items]
Revenue	16,872	18,028	35,053	34,187
Physician Staffing | Temporary Staffing Services
Disaggregation of Revenue [Line Items]
Revenue	16,081	16,827	33,241	31,981
Physician Staffing | Other Services
Disaggregation of Revenue [Line Items]
Revenue	791	1,201	1,812	2,206
Search
Disaggregation of Revenue [Line Items]
Revenue	1,809	3,942	5,459	7,317
Search | Temporary Staffing Services
Disaggregation of Revenue [Line Items]
Revenue	0	0	0	0
Search | Other Services
Disaggregation of Revenue [Line Items]
Revenue	$ 1,809	$ 3,942	$ 5,459	$ 7,317