Note 8 - Employee Benefit Plans (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Contribution Plan, Cost	$ 24.5	$ 20.8	$ 19.7
Deferred Compensation Liability, Current and Noncurrent, Total	23.1	20.4
Other Current Assets [Member] | Defined Benefit Plan, Equity Securities [Member]
Defined Benefit Plan, Plan Assets, Investment within Plan Asset Category, Amount	$ 23.1	$ 20.4