REVENUE - Summary of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Revenues	$ 210,758	$ 206,715	$ 638,976	$ 648,484
Non-Destructive Evaluation and Testing Services
Disaggregation of Revenue [Line Items]
Revenues	83,461	83,207	254,584	259,118
Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues	100,782	101,663	312,665	323,745
Heat Treating
Disaggregation of Revenue [Line Items]
Revenues	18,399	13,001	49,697	42,935
Other
Disaggregation of Revenue [Line Items]
Revenues	8,116	8,844	22,030	22,686
IHT
Disaggregation of Revenue [Line Items]
Revenues	107,604	103,857	320,286	322,426
IHT | Non-Destructive Evaluation and Testing Services
Disaggregation of Revenue [Line Items]
Revenues	83,461	83,207	254,584	259,118
IHT | Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues	2	39	149	261
IHT | Heat Treating
Disaggregation of Revenue [Line Items]
Revenues	18,036	12,946	48,979	42,391
IHT | Other
Disaggregation of Revenue [Line Items]
Revenues	6,105	7,665	16,574	20,656
MS
Disaggregation of Revenue [Line Items]
Revenues	103,154	102,858	318,690	326,058
MS | Non-Destructive Evaluation and Testing Services
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
MS | Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues	100,780	101,624	312,516	323,484
MS | Heat Treating
Disaggregation of Revenue [Line Items]
Revenues	363	55	718	544
MS | Other
Disaggregation of Revenue [Line Items]
Revenues	2,011	1,179	5,456	2,030
United States and Canada
Disaggregation of Revenue [Line Items]
Revenues	172,871	168,086	527,475	534,287
United States and Canada | IHT
Disaggregation of Revenue [Line Items]
Revenues	104,478	100,800	310,985	312,344
United States and Canada | MS
Disaggregation of Revenue [Line Items]
Revenues	68,393	67,286	216,490	221,943
Other Countries
Disaggregation of Revenue [Line Items]
Revenues	37,887	38,629	111,501	114,197
Other Countries | IHT
Disaggregation of Revenue [Line Items]
Revenues	3,126	3,057	9,301	10,082
Other Countries | MS
Disaggregation of Revenue [Line Items]
Revenues	$ 34,761	$ 35,572	$ 102,200	$ 104,115