Note 3 - Long-term Debt (Details Textual) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Line of Credit Facility, Maximum Borrowing Capacity	$ 30.0
Letters of Credit Outstanding, Amount	20.7	$ 16.1
Line of Credit Facility, Remaining Borrowing Capacity	$ 9.3
Line of Credit Facility, Dividends Payment, Maximum		$ 150.0
Line Of Credit Facility Dividend Restrictions Percentage Of Net Income Limit		25.00%
Line of Credit Facility Dividend Restrictions Percentage of Net Income Limit1		25.00%
Line of Credit Facility, Waiver to Pay Dividends, Maximum		$ 80.0	$ 80.0
Credit Facility [Member]
Long-Term Debt, Weighted Average Interest Rate, at Point in Time	8.50%