REVENUE - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Disaggregation of Revenue [Line Items]
Revenues	$ 247,780	$ 217,410	$ 717,621	$ 650,901
Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	218,339	197,879	628,917	591,043
Non-Destructive Evaluation and Testing Services | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	87,267	80,553	255,419	244,374
Repair and Maintenance Services | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	106,795	95,616	305,435	279,029
Heat Treating | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	16,482	11,999	46,221	43,418
Other | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	7,795	9,711	21,842	24,222
United States and Canada | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	184,144	162,697	530,677	492,105
Other Countries | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	34,195	35,182	98,240	98,938
IHT | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	110,312	101,476	320,033	310,077
IHT | Non-Destructive Evaluation and Testing Services | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	87,267	80,553	255,419	244,374
IHT | Repair and Maintenance Services | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	19	56	158	344
IHT | Heat Treating | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	16,357	11,928	45,983	42,650
IHT | Other | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	6,669	8,939	18,473	22,709
IHT | United States and Canada | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	108,009	98,812	312,928	302,871
IHT | Other Countries | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	2,303	2,664	7,105	7,206
MS | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	108,027	96,403	308,884	280,966
MS | Non-Destructive Evaluation and Testing Services | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
MS | Repair and Maintenance Services | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	106,776	95,560	305,277	278,685
MS | Heat Treating | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	125	71	238	768
MS | Other | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	1,126	772	3,369	1,513
MS | United States and Canada | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	76,135	63,885	217,749	189,234
MS | Other Countries | Continuing Operations
Disaggregation of Revenue [Line Items]
Revenues	$ 31,892	$ 32,518	$ 91,135	$ 91,732