STOCK-BASED COMPENSATION - Vesting Conditions (Details)	3 Months Ended	6 Months Ended
	Jun. 30, 2021 shares	Jun. 30, 2021 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Number of share of restricted stock (shares)		152,171
Restricted stock units, type 1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Number of share of restricted stock (shares)		66,220
Target, Regional adjusted EBITDA, percentage	70.00%	70.00%
Target, Group adjusted EBITDA, percentage	30.00%	30.00%
Restricted stock units, type 1 | Performance Conditions, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target, Group adjusted EBITDA, percentage	75.00%	75.00%
Target, Corporate costs , percentage	25.00%	25.00%
Restricted stock units, type 1 | Performance Conditions, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target, Group adjusted EBITDA, percentage	100.00%	100.00%
Restricted stock units, type 1 | First Anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Number of share of restricted stock (shares)	53,075
Vesting rights, percentage		33.00%
Restricted stock units, type 1 | Second Anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights, percentage		33.00%
Restricted stock units, type 1 | Third Anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights, percentage		34.00%
Restricted stock units, type 2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Number of share of restricted stock (shares)		60,451
Restricted stock units, type 2 | First Anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights, percentage		66.60%
Restricted stock units, type 2 | Second Anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Number of share of restricted stock (shares)	73,596
Vesting rights, percentage		16.70%
Restricted stock units, type 2 | Third Anniversary
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights, percentage		16.70%
Restricted stock units, time
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Number of share of restricted stock (shares)		25,500
Restricted stock units, time | Performance Conditions, 2021 | Coit Staffing, Inc.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target, Group adjusted EBITDA, percentage	100.00%	100.00%