Note 5 - Derivative and Other Hedging Instruments (Details Textual) $ in Millions	Sep. 30, 2023 USD ($) $ / item	Dec. 31, 2022 USD ($) $ / item
Five Year Treasury Note Futures [Member] \| Short [Member]
Derivative, Forward Price (in USD per Per Share) \| $ / item	105.4	107.9
Derivative, Fair Value, Net	$ 496.7	$ 810.0
Derivative, Notional Amount	$ 471.5	$ 750.5
Ten Year T-Note Futures [Member] \| Short [Member]
Derivative, Forward Price (in USD per Per Share) \| $ / item	108.1
Derivative, Fair Value, Net	$ 426.8
Derivative, Notional Amount	395.0
Interest Rate Swap Accruing October 23, 2023 [Member]
Derivative, Notional Amount	$ 175.0
Derivative, Fixed Interest Rate	3.53%
Interest Rate Swap Accruing February 24, 2024 [Member]
Derivative, Notional Amount	$ 274.0
Derivative, Fixed Interest Rate	3.43%

Fair value of the assets less the liabilities of a derivative or group of derivatives.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482907/825-10-50-10

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Fixed interest rate related to the interest rate derivative.

+ References

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The forward price on the price risk forward or futures contract, such as a gas futures contract.

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Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-1B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-1A

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