REVENUE - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Revenues	$ 862,615	$ 840,208
Non-Destructive Evaluation and Testing Services
Disaggregation of Revenue [Line Items]
Revenues	343,713	336,821
Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues	429,755	413,604
Heat Treating
Disaggregation of Revenue [Line Items]
Revenues	60,101	61,802
Other
Disaggregation of Revenue [Line Items]
Revenues	29,046	27,981
IHT
Disaggregation of Revenue [Line Items]
Revenues	429,559	422,562
IHT | Non-Destructive Evaluation and Testing Services
Disaggregation of Revenue [Line Items]
Revenues	343,713	336,821
IHT | Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues	275	180
IHT | Heat Treating
Disaggregation of Revenue [Line Items]
Revenues	59,399	61,526
IHT | Other
Disaggregation of Revenue [Line Items]
Revenues	26,172	24,035
MS
Disaggregation of Revenue [Line Items]
Revenues	433,056	417,646
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	429,480	413,424
MS | Heat Treating
Disaggregation of Revenue [Line Items]
Revenues	702	276
MS | Other
Disaggregation of Revenue [Line Items]
Revenues	2,874	3,946
United States and Canada
Disaggregation of Revenue [Line Items]
Revenues	708,633	708,812
United States and Canada | IHT
Disaggregation of Revenue [Line Items]
Revenues	414,515	412,661
United States and Canada | MS
Disaggregation of Revenue [Line Items]
Revenues	294,118	296,151
Other Countries
Disaggregation of Revenue [Line Items]
Revenues	153,982	131,396
Other Countries | IHT
Disaggregation of Revenue [Line Items]
Revenues	15,044	9,901
Other Countries | MS
Disaggregation of Revenue [Line Items]
Revenues	$ 138,938	$ 121,495