Note 4 - Employee Benefit Plans (Details Textual) - USD ($) $ in Millions	1 Months Ended		3 Months Ended		6 Months Ended
	May 31, 2022	Jan. 31, 2021	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Pension Plan [Member]
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 5.6
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Plan Assets, Contributions by Employer		$ 16.8
Nonoperating Income (Expense) [Member]
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component			$ 1.4	$ 0.2	$ 2.7	$ 0.3