Note 6 - Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Insurance accruals	$ 69,168	$ 58,614
Allowance for doubtful accounts	12,584	10,766
Compensation accrual	9,882	8,003
Deferred compensation accrual	26,805	36,309
Federal benefit of state uncertain tax positions	17,693	17,491
Lease liabilities	74,858	82,048
State NOL carry-forward	4,235	5,478
Other	3,815	3,890
Total gross deferred tax assets	219,040	222,599
Valuation allowance	(4,235)	(5,478)
Total deferred tax assets, net of valuation allowance	214,805	217,121
Plant and equipment, principally due to differences in depreciation	1,001,537	1,057,922
Prepaid permits and insurance, principally due to expensing for income tax purposes	35,592	63,880
Lease right-of-use assets	73,925	81,416
Total gross deferred tax liabilities	1,111,054	1,203,218
Net deferred tax liability	$ 896,249	$ 986,097