Note 5 - Derivative and Other Hedging Instruments (Details Textual) $ in Millions	Dec. 31, 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	108.77	107.93
Derivative, Fair Value, Net	$ 458.5	$ 810.0
Derivative, Notional Amount	$ 421.5	$ 750.5
Ten Year Ultra Future [Member] \| Short [Member]
Derivative, Forward Price (in USD per Per Share) \| $ / item	112.89	118.28
Derivative, Fair Value, Net	$ 361.3	$ 206.4
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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- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

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- Definition

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

+ References

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- Definition

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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