Note 7 - Income Taxes (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Deferred Tax Assets, Valuation Allowance	$ 0	$ 0
Income Tax Examination, Penalties and Interest Accrued Liabilities (Receivables)	(4,000)	(3,000)
Income Tax Examination, Penalties and Interest Expense (Benefit)	(1,000)	(2,000)	$ (5,000)
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	30,000	31,000	31,000
State and Local Jurisdiction [Member] | Nebraska, Iowa, Kansas, and Arkansas Department of Revenue [Member]
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability	$ (114,000)
State and Local Jurisdiction [Member] | Nebraska, Iowa, Arkansas, and Idaho Department of Revenue [Member]
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability		$ (95,000)
State and Local Jurisdiction [Member] | Nebraska, Oklahoma, Idaho, Louisiana and Arkansas Department of Revenue [Member]
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability			$ (32,000)