Note 21 - Incentive Plans (Details Textual) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	May 31, 2020
Share-based Payment Arrangement, Expense		$ 23.7	$ 20.2	$ 18.2
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total		$ 34.4
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)		2 years 10 months 24 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)		0	0	0
Share-based Payment Arrangement, Option, Exercise Price Range, Lower Range Limit (in dollars per share)		$ 15.09
Share-based Payment Arrangement, Option, Exercise Price Range, Upper Range Limit (in dollars per share)		$ 24.12
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term (Year)		1 year 4 months 24 days
Proceeds from Stock Options Exercised		$ 1.0	$ 3.9	$ 0.6
Common Stock, Shares, Issued, Total (in shares)		432,518,743	431,814,951
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent		5.00%
Defined Contribution Plan, Cost		$ 2.3	$ 2.2	2.2
Employee [Member]
Severance Costs		$ 8.7	$ 2.6	$ 3.8
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 (in dollars per share)		$ 18.67	$ 18.03	$ 14.72
Dividend, Share-based Payment Arrangement, Shares		$ 2.2	$ 3.0	$ 2.8
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 (in dollars per share)		$ 18.02	$ 22.00	$ 15.40
Common Stock, Shares, Issued, Total (in shares)		594,900	104,551	0
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	[1]	0.00%	0.00%	0.00%
The 2020 Equity Participation Plan [Member]
Common Stock, Capital Shares Reserved for Future Issuance (in shares)					10,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)		9,980,000

[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.