Note 10 - Debt - Short-term and Long-term Debt (Details) (Parentheticals) - USD ($) $ in Millions	Sep. 30, 2020	May 08, 2020	Dec. 31, 2019
The 5.800% Senior Note [Member]
Interest rate	5.80%		5.80%
Unamortized discount	$ 0.3		$ 0.7
The 3.625% Senior Note [Member]
Interest rate	3.625%	3.625%
Unamortized discount		$ 5.2
Unamortized premium	$ 10.9
The 4.125% Senior Note [Member]
Interest rate	4.125%		4.125%
Unamortized premium	$ 12.8		$ 13.9
The 4.000% Senior Note [Member]
Interest rate	4.00%		4.00%
Unamortized discount	$ 5.7		$ 6.7
The 5.500% Senior Note [Member]
Interest rate	5.50%		5.50%
Unamortized discount	$ 4.3		$ 4.5
The 4.125% Senior Note Maturing September 12, 2022 [Member]
Interest rate	4.125%		4.125%
Unamortized discount	$ 1.2		$ 1.6