REVENUE - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenues	$ 218,576	$ 194,618
Non-Destructive Evaluation and Testing Services
Disaggregation of Revenue [Line Items]
Revenues	105,989	87,613
Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues	91,794	86,057
Heat Treating
Disaggregation of Revenue [Line Items]
Revenues	13,896	14,144
Other
Disaggregation of Revenue [Line Items]
Revenues	6,897	6,804
United States and Canada
Disaggregation of Revenue [Line Items]
Revenues	171,998	158,326
Other Countries
Disaggregation of Revenue [Line Items]
Revenues	46,578	36,292
IHT
Disaggregation of Revenue [Line Items]
Revenues	95,595	91,139
IHT | Non-Destructive Evaluation and Testing Services
Disaggregation of Revenue [Line Items]
Revenues	76,449	71,530
IHT | Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues	24	81
IHT | Heat Treating
Disaggregation of Revenue [Line Items]
Revenues	13,839	13,455
IHT | Other
Disaggregation of Revenue [Line Items]
Revenues	5,283	6,073
IHT | United States and Canada
Disaggregation of Revenue [Line Items]
Revenues	93,376	89,225
IHT | Other Countries
Disaggregation of Revenue [Line Items]
Revenues	2,219	1,914
MS
Disaggregation of Revenue [Line Items]
Revenues	93,441	87,396
MS | Non-Destructive Evaluation and Testing Services
Disaggregation of Revenue [Line Items]
Revenues	0	0
MS | Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues	91,770	85,976
MS | Heat Treating
Disaggregation of Revenue [Line Items]
Revenues	57	689
MS | Other
Disaggregation of Revenue [Line Items]
Revenues	1,614	731
MS | United States and Canada
Disaggregation of Revenue [Line Items]
Revenues	63,931	60,046
MS | Other Countries
Disaggregation of Revenue [Line Items]
Revenues	29,510	27,350
Quest Integrity
Disaggregation of Revenue [Line Items]
Revenues	29,540	16,083
Quest Integrity | Non-Destructive Evaluation and Testing Services
Disaggregation of Revenue [Line Items]
Revenues	29,540	16,083
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
Disaggregation of Revenue [Line Items]
Revenues	0	0
Quest Integrity | United States and Canada
Disaggregation of Revenue [Line Items]
Revenues	14,691	9,055
Quest Integrity | Other Countries
Disaggregation of Revenue [Line Items]
Revenues	$ 14,849	$ 7,028