Note 20 - Incentive Plans (Details Textual) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allocated Share-based Compensation Expense, Total		$ 18.2	$ 21.6	$ 19.1
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total		$ 29.4
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition		2 years 292 days
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		8,926,449	10,410,343	10,015,040
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross		0	0	0
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit		$ 11.54
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit		$ 24.12
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term		2 years 292 days
Proceeds from Stock Options Exercised		$ 0.6	$ 1.5	$ 21.1
Common Stock, Shares, Issued, Total		421,388,879	425,646,380
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent		5.00%
Defined Contribution Plan, Cost		$ 2.2	$ 2.1	2.0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term		2 years 292 days
Employee [Member]
Severance Costs		$ 3.8	$ 5.5	$ 1.7
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 14.72	$ 25.04	$ 26.15
Dividends, Share-based Compensation, Stock		$ 2.8	$ 2.4	$ 2.2
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 15.40	$ 23.35	$ 28.60
Common Stock, Shares, Issued, Total		0	0	130,080
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	[1]	0.00%	0.00%	0.00%

[1] Total Shareholder Returns, as used in the performance share awards computation, are measured based on cumulative dividend stock prices, as such a zero percent dividend yield is utilized.