BUSINESS SEGMENT INFORMATION - Summarized financial information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Revenues:
Revenues	$ 377,833	$ 476,668
Operating income:
Total operating income	32,349	90,657
Pension settlement charges		17,375
Gain on disposition of assets, net	1,214	2,936
Interest expense	(234)	(72)
Interest income	2,965	1,855
Other income, net	767	761
Income before income taxes	35,847	93,201
Depreciation and amortization	30,004	24,125
Capital expenditures	52,778	65,300
Identifiable assets	1,297,233	1,187,830	$ 1,286,845
Technical Services
Revenues:
Revenues	356,394	451,991
Support Services
Revenues:
Revenues	21,439	24,677
Segment reconciling item
Operating income:
Corporate Expense	(4,420)	(5,081)
Pension settlement charges		17,375
Gain on disposition of assets, net	1,214	2,936
Depreciation and amortization	19	13
Capital expenditures	1,096	985
Identifiable assets	320,008	253,611
Operating Segments
Revenues:
Revenues	377,833	476,668
Operating income:
Total operating income	32,349	90,657
Income before income taxes	35,847	93,201
Operating Segments | Technical Services
Revenues:
Revenues	356,394	451,991
Operating income:
Total operating income	31,956	103,533
Depreciation and amortization	27,170	22,008
Capital expenditures	43,869	63,002
Identifiable assets	897,462	851,689
Operating Segments | Support Services
Revenues:
Revenues	21,439	24,677
Operating income:
Total operating income	3,599	6,644
Depreciation and amortization	2,815	2,104
Capital expenditures	7,813	1,313
Identifiable assets	$ 79,763	$ 82,530