Note 7 - Income Taxes (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	35.00%
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability		$ 309.2
Income Taxes Receivable	$ 60.9		$ 102.4
Unrecognized Tax Benefits, Ending Balance	50.6	45.3	52.2	$ 35.4
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	41.8		43.1
Income Tax Examination, Penalties and Interest Accrued, Total	3.2	$ 2.1	2.4
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	$ 4.8		$ 4.6
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member]
Open Tax Year	2016 2017 2018 2019
State and Local Jurisdiction [Member]
Open Tax Year	2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019