GOODWILL AND IMPAIRMENT CHARGES - Goodwill Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Goodwill [Roll Forward]
Balance at beginning of period		$ 282,006		$ 282,006
Acquisitions				496
Foreign currency adjustments				(1,756)
Goodwill impairment loss	$ 0		$ 0	(191,788)	$ 0
Balance at end of period	88,958			88,958
IHT
Goodwill [Roll Forward]
Balance at beginning of period		193,216		193,216
Acquisitions				0
Foreign currency adjustments				(1,428)
Goodwill impairment loss		(191,800)		(191,788)
Balance at end of period	0			0
MS
Goodwill [Roll Forward]
Balance at beginning of period		55,409		55,409
Acquisitions				0
Foreign currency adjustments				(54)
Goodwill impairment loss				0
Balance at end of period	55,355			55,355
Quest Integrity
Goodwill [Roll Forward]
Balance at beginning of period		$ 33,381		33,381
Acquisitions				496
Foreign currency adjustments				(274)
Goodwill impairment loss				0
Balance at end of period	$ 33,603			$ 33,603