Note 7 - Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Beginning balance	$ 50.6	$ 52.2	$ 45.3
Additions based on tax positions related to the current year	9.8	11.0	13.9
Additions based on tax positions taken in prior years	13.9
(Reductions) based on tax positions taken in prior years		(6.5)	(2.4)
Reductions due to settlements	(1.0)	0.0	0.0
Reductions due to lapse of applicable statute of limitations	(7.2)	(6.1)	(4.6)
Ending balance	$ 66.1	$ 50.6	$ 52.2