Note 6 - Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Beginning balance	$ 89.1	$ 78.5	$ 66.1
Additions based on tax positions related to the current year	16.2	25.8	14.9
Additions/(reductions) based on tax positions taken in prior years	0.5	2.8	4.8
Reductions due to settlements	(14.6)	(8.0)	(0.9)
Reductions due to lapse of applicable statute of limitations	(10.3)	(10.0)	(6.4)
Ending balance	$ 80.9	$ 89.1	$ 78.5