Note 7 - Income Taxes (Details Textual) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			35.00%
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability	$ (309.2)		$ (309.2)
Income Taxes Receivable	61.3		61.3	$ 15.7
Unrecognized Tax Benefits	45.3		45.3	35.4	$ 32.0	$ 31.6
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	37.5		37.5	23.0
Income Tax Examination, Penalties and Interest Accrued	2.1		2.1	1.9	$ 1.9
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	$ 3.6		$ 3.6	$ 4.4
Scenario, Forecast [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%