Note 6 - Income Taxes (Detail) - Deferred Tax Assets and Liabilities (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Insurance accruals	$ 9,713	$ 8,316
Allowance for doubtful accounts	1,715	1,827
Compensation accrual	16,851	20,522
Deferred compensation accrual	25,997	24,727
Federal benefit of state uncertain tax positions	10,586	7,155
Equity investment	2,197	2,197
Other	3,403	3,584
Total gross deferred tax assets	70,462	68,328
Valuation allowance	(2,749)	(2,749)
Total deferred tax assets, net of valuation allowance	67,713	65,579
Plant and equipment, principally due to differences in depreciation	571,830	551,526
Prepaid permits and insurance, principally due to expensing for income tax purposes	19,069	17,605
Other	9,188	8,027
Total gross deferred tax liabilities	600,087	577,158
Net deferred tax liability	$ 532,374	$ 511,579