Note 5 - Income Taxes - Net Deferred Tax Liability (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Reserves and accrued liabilities	$ 11,975	$ 12,050
Other	1,597	1,768
Deferred Tax Assets, Gross, Total	13,572	13,818
Deferred tax liabilities:
Depreciation	135,306	131,650
Prepaid expenses	3,429	3,266
Deferred Tax Liabilities, Gross, Total	138,735	134,916
Net deferred tax liability	$ 125,163	$ 121,098