BUSINESS SEGMENT INFORMATION - Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Revenues:
Revenues	$ 330,417	$ 459,601	$ 1,222,943	$ 1,119,732
Operating income:
Operating income	22,711	92,170	195,737	175,620
Pension settlement charges			(18,286)
Gain on disposition of assets, net	1,778	1,543	7,729	6,295
Interest expense	(101)	(143)	(246)	(543)
Interest income	1,450	329	6,003	472
Other income (expense), net	804	(67)	2,196	516
Income before income taxes	24,864	92,289	203,690	176,065
Depreciation and amortization	28,388	20,941	78,716	60,501
Capital expenditures			148,816	90,227
Identifiable assets	1,247,373	1,055,583	1,247,373	1,055,583	$ 1,129,013
Technical Services
Revenues:
Revenues	303,069	435,775	1,145,078	1,058,227
Operating income:
Operating income	18,912	89,455	199,462	171,093
Support Services
Revenues:
Revenues	27,348	23,826	77,865	61,505
Operating income:
Operating income	6,861	5,278	21,425	11,392
Segment reconciling item
Operating income:
Corporate expenses	(4,840)	(4,106)	(14,593)	(13,160)
Pension settlement charges			(18,286)
Gain on disposition of assets, net	1,778	1,543	7,729	6,295
Depreciation and amortization			38	153
Capital expenditures			3,420	841
Identifiable assets	289,398	139,727	289,398	139,727
Operating Segments
Revenues:
Revenues	330,417	459,601	1,222,943	1,119,732
Operating income:
Operating income	22,711	92,170	195,737	175,620
Income before income taxes	24,864	92,289	203,690	176,065
Operating Segments | Technical Services
Operating income:
Depreciation and amortization			71,175	53,002
Capital expenditures			136,237	79,828
Identifiable assets	873,819	836,310	873,819	836,310
Operating Segments | Support Services
Operating income:
Depreciation and amortization			7,503	7,346
Capital expenditures			9,159	9,558
Identifiable assets	$ 84,156	$ 79,546	$ 84,156	$ 79,546