REVENUE - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Revenues	$ 840,208	$ 794,197
Non-Destructive Evaluation and Testing Services
Disaggregation of Revenue [Line Items]
Revenues	336,821	325,204
Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues	413,604	375,352
Heat Treating
Disaggregation of Revenue [Line Items]
Revenues	61,802	60,661
Other
Disaggregation of Revenue [Line Items]
Revenues	27,981	32,980
IHT
Disaggregation of Revenue [Line Items]
Revenues	422,562	415,371
IHT | Non-Destructive Evaluation and Testing Services
Disaggregation of Revenue [Line Items]
Revenues	336,821	325,204
IHT | Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues	180	467
IHT | Heat Treating
Disaggregation of Revenue [Line Items]
Revenues	61,526	59,855
IHT | Other
Disaggregation of Revenue [Line Items]
Revenues	24,035	29,845
MS
Disaggregation of Revenue [Line Items]
Revenues	417,646	378,826
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	413,424	374,885
MS | Heat Treating
Disaggregation of Revenue [Line Items]
Revenues	276	806
MS | Other
Disaggregation of Revenue [Line Items]
Revenues	3,946	3,135
United States and Canada
Disaggregation of Revenue [Line Items]
Revenues	708,812	661,813
United States and Canada | IHT
Disaggregation of Revenue [Line Items]
Revenues	412,661	405,007
United States and Canada | MS
Disaggregation of Revenue [Line Items]
Revenues	296,151	256,806
Other Countries
Disaggregation of Revenue [Line Items]
Revenues	131,396	132,384
Other Countries | IHT
Disaggregation of Revenue [Line Items]
Revenues	9,901	10,364
Other Countries | MS
Disaggregation of Revenue [Line Items]
Revenues	$ 121,495	$ 122,020