Income Taxes (Summary of the Total Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets
Lease liabilities	$ 22,265	$ 21,880
Tax carryforwards	14,816	12,398
Inventories	4,880	5,571
Accrued liabilities	9,226	8,176
Employee benefits	3,319	3,086
Land valuation adjustment	6,378	6,261
Partnership investment - development costs	12,565	0
Other	9,680	6,850
Total deferred tax assets	83,129	64,222
Less: Valuation allowance	11,783	11,809
Deferred tax assets, net of valuation allowance	71,346	52,413
Deferred tax liabilities
Lease right-of-use assets	22,611	21,880
Depreciation and depletion	23,607	19,665
Partnership investment - development costs	0	6,069
Accrued pension benefits	10,047	10,921
Total deferred tax liabilities	56,265	58,535
Net deferred asset (liability)	$ 15,081
Net deferred asset (liability)		$ (6,122)