REVENUE - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018	[1]
Disaggregation of Revenue [Line Items]
Revenues	$ 207,303	$ 219,093	$ 189,304	$ 236,839	$ 287,807	$ 290,079	$ 315,829	$ 269,599	$ 852,539	[1]	$ 1,163,314	[1]	$ 1,246,929
United States and Canada
Disaggregation of Revenue [Line Items]
Revenues									693,846		965,959
Other Countries
Disaggregation of Revenue [Line Items]
Revenues									158,693		197,355
Asset Integrity Management
Disaggregation of Revenue [Line Items]
Revenues									380,153		524,405
Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues									388,519		527,775
Heat Treating
Disaggregation of Revenue [Line Items]
Revenues									51,308		74,462
Other Services
Disaggregation of Revenue [Line Items]
Revenues									32,559		36,672
IHT
Disaggregation of Revenue [Line Items]
Revenues									374,740		512,950
IHT | United States and Canada
Disaggregation of Revenue [Line Items]
Revenues									365,847		496,789
IHT | Other Countries
Disaggregation of Revenue [Line Items]
Revenues									8,893		16,161
IHT | Asset Integrity Management
Disaggregation of Revenue [Line Items]
Revenues									294,838		409,413
IHT | Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues									206		755
IHT | Heat Treating
Disaggregation of Revenue [Line Items]
Revenues									50,220		71,689
IHT | Other Services
Disaggregation of Revenue [Line Items]
Revenues									29,476		31,093
MS
Disaggregation of Revenue [Line Items]
Revenues									392,484		535,372
MS | United States and Canada
Disaggregation of Revenue [Line Items]
Revenues									278,882		393,120
MS | Other Countries
Disaggregation of Revenue [Line Items]
Revenues									113,602		142,252
MS | Asset Integrity Management
Disaggregation of Revenue [Line Items]
Revenues									0		0
MS | Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues									388,313		527,020
MS | Heat Treating
Disaggregation of Revenue [Line Items]
Revenues									1,088		2,773
MS | Other Services
Disaggregation of Revenue [Line Items]
Revenues									3,083		5,579
Quest Integrity
Disaggregation of Revenue [Line Items]
Revenues									85,315		114,992
Quest Integrity | United States and Canada
Disaggregation of Revenue [Line Items]
Revenues									49,117		76,050
Quest Integrity | Other Countries
Disaggregation of Revenue [Line Items]
Revenues									36,198		38,942
Quest Integrity | Asset Integrity Management
Disaggregation of Revenue [Line Items]
Revenues									85,315		114,992
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

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