Asset Retirement Obligations (ARO Activity) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Carrying amount of the asset retirement obligations, balance at beginning of period	$ 46,002	$ 43,951
Liabilities settled during the period	(1,900)	(1,179)
Liabilities incurred during the period	1,920
Accretion expense	3,528	3,522
Revision of estimated cash flows	3,063	(292)
Carrying amount of the asset retirement obligations, balance at end of period	52,613	46,002
Operating Segments | Coal Mining customer
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Carrying amount of the asset retirement obligations, balance at beginning of period	28,460	26,898
Liabilities settled during the period	(852)	(223)
Liabilities incurred during the period	1,920
Accretion expense	2,170	2,190
Revision of estimated cash flows	1,346	(405)
Carrying amount of the asset retirement obligations, balance at end of period	33,044	28,460
Unallocated Items
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Carrying amount of the asset retirement obligations, balance at beginning of period	17,542	17,053
Liabilities settled during the period	(1,048)	(956)
Liabilities incurred during the period	0
Accretion expense	1,358	1,332
Revision of estimated cash flows	1,717	113
Carrying amount of the asset retirement obligations, balance at end of period	$ 19,569	$ 17,542