SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND PRACTICES - Goodwill Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Goodwill [Roll Forward]
Goodwill, Gross, beginning balance	$ 358,380
Accumulated Impairment, beginning balance	(267,029)
Goodwill, Net, beginning balance	91,351
Goodwill, Foreign Currency Translation Gain (Loss)	(958)
Goodwill, Gross, ending balance	357,422
Accumulated Impairment, ending balance	(267,029)
Goodwill, Net, ending balance	90,393
Impairment loss	0	$ (191,788)
IHT
Goodwill [Roll Forward]
Goodwill, Gross, beginning balance	212,928
Accumulated Impairment, beginning balance	(212,928)
Goodwill, Net, beginning balance	0
Goodwill, Foreign Currency Translation Gain (Loss)	0
Goodwill, Gross, ending balance	212,928
Accumulated Impairment, ending balance	(212,928)
Goodwill, Net, ending balance	0
Impairment loss	(191,800)
MS
Goodwill [Roll Forward]
Goodwill, Gross, beginning balance	110,721
Accumulated Impairment, beginning balance	(54,101)
Goodwill, Net, beginning balance	56,620
Goodwill, Foreign Currency Translation Gain (Loss)	(559)
Goodwill, Gross, ending balance	110,162
Accumulated Impairment, ending balance	(54,101)
Goodwill, Net, ending balance	56,061
Quest Integrity
Goodwill [Roll Forward]
Goodwill, Gross, beginning balance	34,731
Accumulated Impairment, beginning balance	0
Goodwill, Net, beginning balance	34,731
Goodwill, Foreign Currency Translation Gain (Loss)	(399)
Goodwill, Gross, ending balance	34,332
Accumulated Impairment, ending balance	0
Goodwill, Net, ending balance	$ 34,332