Note 7 - Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Beginning balance	$ 35.4	$ 32.0	$ 31.6
Additions based on tax positions related to the current year	11.6	10.3	9.4
Additions based on tax positions taken in prior years	5.4
(Reductions) based on tax positions taken in prior years		(3.2)	(2.5)
Reductions due to settlements	(2.4)	(0.4)	(3.0)
Reductions due to lapse of applicable statute of limitations	(4.7)	(3.3)	(3.5)
Ending balance	$ 45.3	$ 35.4	$ 32.0