Unconsolidated Subsidiaries (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Variable Interest Entity [Line Items]
Variable interest entity, reporting entity involvement, maximum risk of loss	$ 5,700		$ 5,700		$ 5,500
Earnings of unconsolidated operations	16,494	$ 15,155	45,618	$ 42,054
Utility Coal Mining and Contract Mining Member
Variable Interest Entity [Line Items]
Earnings of unconsolidated operations	$ 15,400	$ 14,900	$ 43,700	$ 41,800
Unconsolidated Subsidiaries
Variable Interest Entity [Line Items]
Ownership percentage	100.00%		100.00%
Income from equity method investee	$ 18,560		$ 18,560		14,137
Other Noncurrent Assets
Variable Interest Entity [Line Items]
Income from equity method investee	$ 18,600		$ 18,600		$ 14,100