GOODWILL AND IMPAIRMENT CHARGES (Details) - USD ($) $ in Thousands		12 Months Ended
	Dec. 01, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Roll Forward]
Goodwill, Gross, beginning balance		$ 357,247	$ 356,891
Accumulated Impairment, beginning balance		(75,241)	(75,241)
Goodwill, Net, beginning balance		282,006	281,650
FX Adjustments		637	356
Impairment charge	$ 0	(191,788)	0	$ 0
Additions		496
Goodwill, Gross, ending balance		358,380	357,247	356,891
Accumulated Impairment, ending balance		(267,029)	(75,241)	(75,241)
Goodwill, Net, ending balance		91,351	282,006	281,650
IHT
Goodwill [Roll Forward]
Goodwill, Gross, beginning balance		214,356	213,748
Accumulated Impairment, beginning balance		(21,140)	(21,140)
Goodwill, Net, beginning balance		193,216	192,608
FX Adjustments		(1,428)	608
Impairment charge		(191,788)
Additions		0
Goodwill, Gross, ending balance		212,928	214,356	213,748
Accumulated Impairment, ending balance		(212,928)	(21,140)	(21,140)
Goodwill, Net, ending balance		0	193,216	192,608
MS
Goodwill [Roll Forward]
Goodwill, Gross, beginning balance		109,510	109,728
Accumulated Impairment, beginning balance		(54,101)	(54,101)
Goodwill, Net, beginning balance		55,409	55,627
FX Adjustments		1,211	(218)
Goodwill, Gross, ending balance		110,721	109,510	109,728
Accumulated Impairment, ending balance		(54,101)	(54,101)	(54,101)
Goodwill, Net, ending balance		56,620	55,409	55,627
Quest Integrity
Goodwill [Roll Forward]
Goodwill, Gross, beginning balance		33,381	33,415
Accumulated Impairment, beginning balance		0	0
Goodwill, Net, beginning balance		33,381	33,415
FX Adjustments		854	(34)
Impairment charge		0
Additions		496
Goodwill, Gross, ending balance		34,731	33,381	33,415
Accumulated Impairment, ending balance		0	0	0
Goodwill, Net, ending balance		$ 34,731	$ 33,381	$ 33,415