RESTRUCTURING AND OTHER RELATED CHARGES (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Restructuring Cost and Reserve [Line Items]
Restructuring and other related charges, net	$ 457	$ 319	$ 2,614	$ 3,365
Operating Group Reorganization Program
Restructuring Cost and Reserve [Line Items]
Restructuring and other related charges, net	457	0	2,614	0
Professional fees	200		1,700
Operating Group Reorganization Program | Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and other related charges, net			2,614
Operating Group Reorganization Program | Employee Severance | Corporate and shared support services
Restructuring Cost and Reserve [Line Items]
Restructuring and other related charges, net	204	0	1,459	0
OneTEAM Program | Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and other related charges, net	0	300	0	3,400
Severance charges incurred cumulatively to date	11,800		11,800
IHT | Operating Group Reorganization Program | Employee Severance | Operating segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other related charges, net	91	0	374	0
MS | Operating Group Reorganization Program | Employee Severance | Operating segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other related charges, net	139	0	484	0
Quest Integrity | Operating Group Reorganization Program | Employee Severance | Operating segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other related charges, net	$ 23	$ 0	$ 297	$ 0