CUSTOMER CONTRACTS - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 210,064	$ 195,171
Temporary Staffing Services
Disaggregation of Revenue [Line Items]
Revenue	202,109	187,816
Other Services
Disaggregation of Revenue [Line Items]
Revenue	7,955	7,355
Nurse And Allied Staffing
Disaggregation of Revenue [Line Items]
Revenue	188,233	175,637
Nurse And Allied Staffing | Temporary Staffing Services
Disaggregation of Revenue [Line Items]
Revenue	184,949	172,662
Nurse And Allied Staffing | Other Services
Disaggregation of Revenue [Line Items]
Revenue	3,284	2,975
Physician Staffing
Disaggregation of Revenue [Line Items]
Revenue	18,181	16,159
Physician Staffing | Temporary Staffing Services
Disaggregation of Revenue [Line Items]
Revenue	17,160	15,154
Physician Staffing | Other Services
Disaggregation of Revenue [Line Items]
Revenue	1,021	1,005
Search
Disaggregation of Revenue [Line Items]
Revenue	3,650	3,375
Search | Temporary Staffing Services
Disaggregation of Revenue [Line Items]
Revenue	0	0
Search | Other Services
Disaggregation of Revenue [Line Items]
Revenue	$ 3,650	$ 3,375