Note 8 - Employee Benefit Plans (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Contribution Plan, Cost	$ 20.8	$ 19.7	$ 16.7
Deferred Compensation Liability, Current and Noncurrent, Total	20.4	15.7
Other Current Assets [Member] | Defined Benefit Plan, Equity Securities [Member]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	$ 20.4	$ 15.7