REVENUE - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Disaggregation of Revenue [Line Items]
Revenues	$ 202,277	$ 189,036
Non-Destructive Evaluation and Testing Services
Disaggregation of Revenue [Line Items]
Revenues	81,606	76,449
Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues	99,841	91,794
Heat Treating
Disaggregation of Revenue [Line Items]
Revenues	14,006	13,896
Other
Disaggregation of Revenue [Line Items]
Revenues	6,824	6,897
IHT
Disaggregation of Revenue [Line Items]
Revenues	101,829	95,595
IHT | Non-Destructive Evaluation and Testing Services
Disaggregation of Revenue [Line Items]
Revenues	81,606	76,449
IHT | Repair and Maintenance Services
Disaggregation of Revenue [Line Items]
Revenues	3	24
IHT | Heat Treating
Disaggregation of Revenue [Line Items]
Revenues	13,728	13,839
IHT | Other
Disaggregation of Revenue [Line Items]
Revenues	6,492	5,283
MS
Disaggregation of Revenue [Line Items]
Revenues	100,448	93,441
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	99,838	91,770
MS | Heat Treating
Disaggregation of Revenue [Line Items]
Revenues	278	57
MS | Other
Disaggregation of Revenue [Line Items]
Revenues	332	1,614
United States and Canada
Disaggregation of Revenue [Line Items]
Revenues	170,562	157,307
United States and Canada | IHT
Disaggregation of Revenue [Line Items]
Revenues	98,531	93,376
United States and Canada | MS
Disaggregation of Revenue [Line Items]
Revenues	72,031	63,931
Other Countries
Disaggregation of Revenue [Line Items]
Revenues	31,715	31,729
Other Countries | IHT
Disaggregation of Revenue [Line Items]
Revenues	3,298	2,219
Other Countries | MS
Disaggregation of Revenue [Line Items]
Revenues	$ 28,417	$ 29,510