RESTRUCTURING AND OTHER RELATED CHARGES (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Restructuring Cost and Reserve [Line Items]
Restructuring and other related charges, net	$ 280	$ 2,860	$ 2,157	$ 3,046
Operating Group Reorganization Program
Restructuring Cost and Reserve [Line Items]
Restructuring and other related charges, net	280	0	2,157	0
Professional fees	700		1,500
Operating Group Reorganization Program | Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and other related charges, net			2,157
Operating Group Reorganization Program | Employee Severance | Corporate and shared support services
Restructuring Cost and Reserve [Line Items]
Restructuring and other related charges, net	33	0	1,255	0
OneTEAM Program | Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and other related charges, net	0	2,900	0	3,100
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	0	0	283	0
MS | Operating Group Reorganization Program | Employee Severance | Operating segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other related charges, net	206	0	345	0
Quest Integrity | Operating Group Reorganization Program | Employee Severance | Operating segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other related charges, net	$ 41	$ 0	$ 274	$ 0