Note 12 - Incentive Plans (Details Textual) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	May 31, 2020
Share-based Payment Arrangement, Expense	$ 11.5	$ 10.3
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total	$ 46.3
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	3 years 1 month 6 days
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)	10,000,000.0

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Aggregate number of common shares reserved for future issuance.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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