Note 6 - Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Insurance accruals	$ 54,047	$ 27,487
Allowance for doubtful accounts	10,230	8,886
Compensation accrual	30,492	22,061
CARES Act payroll tax deferral	0	9,955
Deferred compensation accrual	28,249	28,937
Federal benefit of state uncertain tax positions	16,280	12,870
Lease liabilities	71,732	43,850
State NOL carry-forward	6,765	7,303
Other	7,361	5,549
Total gross deferred tax assets	225,156	166,898
Valuation allowance	(6,765)	(7,303)
Total deferred tax assets, net of valuation allowance	218,391	159,595
Deferred tax liabilities:
Plant and equipment, principally due to differences in depreciation	1,011,963	816,744
Prepaid permits and insurance, principally due to expensing for income tax purposes	55,132	44,132
Lease right-of-use assets	71,827	44,161
Total gross deferred tax liabilities	1,138,922	905,037
Net deferred tax liability	$ 920,531	$ 745,442