REVENUE - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 287,807	$ 290,079	$ 315,829	$ 269,599	$ 309,799	$ 290,856	$ 343,889	$ 302,385	$ 1,163,314	$ 1,246,929	$ 1,200,211
United States and Canada
Disaggregation of Revenue [Line Items]
Revenues									965,959	1,048,282
Other Countries
Disaggregation of Revenue [Line Items]
Revenues									197,355	198,647
Asset Integrity Management
Disaggregation of Revenue [Line Items]
Revenues									524,405	591,394
Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues									527,775	551,121
Heat Treating
Disaggregation of Revenue [Line Items]
Revenues									74,462	83,593
Other Services
Disaggregation of Revenue [Line Items]
Revenues									36,672	20,821
IHT
Disaggregation of Revenue [Line Items]
Revenues									512,950	617,378
IHT | United States and Canada
Disaggregation of Revenue [Line Items]
Revenues									496,789	602,615
IHT | Other Countries
Disaggregation of Revenue [Line Items]
Revenues									16,161	14,763
IHT | Asset Integrity Management
Disaggregation of Revenue [Line Items]
Revenues									409,413	493,806
IHT | Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues									755	27,420
IHT | Heat Treating
Disaggregation of Revenue [Line Items]
Revenues									71,689	80,840
IHT | Other Services
Disaggregation of Revenue [Line Items]
Revenues									31,093	15,312
MS
Disaggregation of Revenue [Line Items]
Revenues									535,372	532,365
MS | United States and Canada
Disaggregation of Revenue [Line Items]
Revenues									393,120	383,405
MS | Other Countries
Disaggregation of Revenue [Line Items]
Revenues									142,252	148,960
MS | Asset Integrity Management
Disaggregation of Revenue [Line Items]
Revenues									0	402
MS | Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues									527,020	523,701
MS | Heat Treating
Disaggregation of Revenue [Line Items]
Revenues									2,773	2,753
MS | Other Services
Disaggregation of Revenue [Line Items]
Revenues									5,579	5,509
Quest Integrity
Disaggregation of Revenue [Line Items]
Revenues									114,992	97,186
Quest Integrity | United States and Canada
Disaggregation of Revenue [Line Items]
Revenues									76,050	62,262
Quest Integrity | Other Countries
Disaggregation of Revenue [Line Items]
Revenues									38,942	34,924
Quest Integrity | Asset Integrity Management
Disaggregation of Revenue [Line Items]
Revenues									114,992	97,186
Quest Integrity | Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues									0	0
Quest Integrity | Heat Treating
Disaggregation of Revenue [Line Items]
Revenues									0	0
Quest Integrity | Other Services
Disaggregation of Revenue [Line Items]
Revenues									$ 0	$ 0