SEGMENT AND GEOGRAPHIC DISCLOSURES - Segment Data for our Three Operating Segments (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2019		Jun. 30, 2018	Jun. 30, 2019		Jun. 30, 2018
Segment Reporting Information [Line Items]
Revenues	$ 315,829		$ 343,889	$ 585,428		$ 646,274
Operating income (loss)	13,004		1,799	(3,524)		(12,326)
Capital expenditures	8,892	[1]	6,595	15,502	[1]	12,082
Depreciation and amortization	12,379		15,979	24,650		32,434
IHT
Segment Reporting Information [Line Items]
Revenues	138,658		168,673	265,714		320,092
MS
Segment Reporting Information [Line Items]
Revenues	144,897		148,978	266,423		281,879
Quest Integrity
Segment Reporting Information [Line Items]
Revenues	32,274		26,238	53,291		44,303
Operating segments | IHT
Segment Reporting Information [Line Items]
Revenues	138,658		168,673	265,714		320,092
Operating income (loss)	9,497		13,281	11,218		20,021
Capital expenditures	2,083	[1]	2,063	3,051	[1]	4,398
Depreciation and amortization	4,401		4,725	8,903		9,530
Operating segments | MS
Segment Reporting Information [Line Items]
Revenues	144,897		148,978	266,423		281,879
Operating income (loss)	20,317		10,582	25,851		13,100
Capital expenditures	2,624	[1]	2,369	4,587	[1]	4,025
Depreciation and amortization	5,518		8,944	10,932		18,222
Operating segments | Quest Integrity
Segment Reporting Information [Line Items]
Revenues	32,274		26,238	53,291		44,303
Operating income (loss)	9,324		5,751	10,968		6,845
Capital expenditures	1,249	[1]	1,031	2,577	[1]	1,652
Depreciation and amortization	999		966	1,920		1,965
Corporate and shared support services
Segment Reporting Information [Line Items]
Operating income (loss)	(26,134)		(27,815)	(51,561)		(52,292)
Capital expenditures	2,936	[1]	1,132	5,287	[1]	2,007
Depreciation and amortization	$ 1,461		$ 1,344	$ 2,895		$ 2,717

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