SEGMENT AND GEOGRAPHIC DISCLOSURES - Segment Data for our Three Operating Segments (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2019		Sep. 30, 2018	Sep. 30, 2019		Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenues	[1]	$ 290,079		$ 290,856	$ 875,507		$ 937,130
Operating income (loss)		(1,840)		(19,694)	(5,364)		(32,020)
Capital expenditures		9,266	[2]	7,312	24,768	[2]	19,394
Depreciation and amortization		12,050		16,032	36,700		48,466
IHT
Segment Reporting Information [Line Items]
Revenues		126,379		147,529	392,093		467,621
MS
Segment Reporting Information [Line Items]
Revenues		135,625		119,011	402,048		400,890
Quest Integrity
Segment Reporting Information [Line Items]
Revenues		28,075		24,316	81,366		68,619
Operating segments | IHT
Segment Reporting Information [Line Items]
Revenues		126,379		147,529	392,093		467,621
Operating income (loss)		6,640		8,754	17,858		28,775
Capital expenditures		2,588	[2]	1,537	5,639	[2]	5,935
Depreciation and amortization		4,390		4,649	13,293		14,179
Operating segments | MS
Segment Reporting Information [Line Items]
Revenues		135,625		119,011	402,048		400,890
Operating income (loss)		15,871		(9,086)	41,722		4,014
Capital expenditures		3,795	[2]	4,930	8,382	[2]	8,955
Depreciation and amortization		5,411		8,911	16,343		27,133
Operating segments | Quest Integrity
Segment Reporting Information [Line Items]
Revenues		28,075		24,316	81,366		68,619
Operating income (loss)		7,122		5,255	18,090		12,100
Capital expenditures		1,038	[2]	610	3,615	[2]	2,262
Depreciation and amortization		814		1,025	2,734		2,990
Corporate and shared support services
Segment Reporting Information [Line Items]
Operating income (loss)		(31,473)		(24,617)	(83,034)		(76,909)
Capital expenditures		1,845	[2]	235	7,132	[2]	2,242
Depreciation and amortization		$ 1,435		$ 1,447	$ 4,330		$ 4,164

[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.