Note 6 - Income Taxes (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%
Income Taxes Receivable	$ 40.7	$ 102.7
Unrecognized Tax Benefits	80.9	89.1	$ 78.5	$ 66.1
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	65.6	72.6
Income Tax Examination, Penalties and Interest Accrued, Total	5.3	4.3	$ 3.5
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	$ 9.0	$ 7.9