Note 6 - Income Taxes (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%
Income Taxes Receivable	$ 102.7	$ 33.7
Unrecognized Tax Benefits, Ending Balance	89.1	78.5	$ 66.1	$ 50.6
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	72.6	67.2
Income Tax Examination, Penalties and Interest Accrued, Total	4.3	3.5	$ 2.9
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	$ 7.9	$ 6.4