SEGMENT AND GEOGRAPHIC DISCLOSURES - Segment Data for our Three Operating Segments (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Revenues	[1]	$ 238,873	$ 189,304	$ 433,491	$ 426,143
Operating income (loss)		(5,994)	(4,366)	(30,294)	(217,298)
Capital expenditures	[2]	5,094	4,808	9,491	11,512
Depreciation and amortization		10,347	11,478	21,306	23,186
IHT
Segment Reporting Information [Line Items]
Revenues		117,462	80,474	208,601	188,355
MS
Segment Reporting Information [Line Items]
Revenues		97,167	92,820	184,563	197,339
Quest Integrity
Segment Reporting Information [Line Items]
Revenues		24,244	16,010	40,327	40,449
Operating segments | IHT
Segment Reporting Information [Line Items]
Revenues		117,462	80,474	208,601	188,355
Operating income (loss)	[3]	7,395	4,740	7,759	(187,410)
Capital expenditures	[2]	2,457	843	5,171	1,884
Depreciation and amortization		3,270	3,746	6,740	7,729
Operating segments | MS
Segment Reporting Information [Line Items]
Revenues		97,167	92,820	184,563	197,339
Operating income (loss)		2,328	9,899	2,443	10,921
Capital expenditures	[2]	1,367	2,446	2,519	6,063
Depreciation and amortization		5,043	5,475	10,482	10,906
Operating segments | Quest Integrity
Segment Reporting Information [Line Items]
Revenues		24,244	16,010	40,327	40,449
Operating income (loss)		5,702	689	5,450	6,795
Capital expenditures	[2]	974	1,044	1,380	2,015
Depreciation and amortization		710	887	1,422	1,773
Corporate and shared support services
Segment Reporting Information [Line Items]
Operating income (loss)		(21,419)	(19,694)	(45,946)	(47,604)
Capital expenditures	[2]	296	475	421	1,550
Depreciation and amortization		$ 1,324	$ 1,370	$ 2,662	$ 2,778

[1] Revenues attributable to individual countries/geographic areas are based on the country of domicile of the legal entity that performs the work.

[2] Totals may vary from amounts presented in the condensed consolidated statements of cash flows due to the timing of cash payments.

[3] Includes goodwill impairment charge for IHT as discussed in Note 1 that impacted operating income (loss) for the six months ended June 30, 2020.