Note 10 - Debt (Details Textual) - USD ($) $ in Millions	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020
Long-term Debt, Gross	$ 2,700.0		$ 3,150.0
Letters of Credit Outstanding, Amount		$ 5.1	5.4
Revolving Credit Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity	1,000.0
Line of Credit Facility, Remaining Borrowing Capacity	$ 604.9		$ 944.6