Counterparty Risk (Exposure to Counterparty Risk) (Details) - Counterparty Risk [Member] $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2024 USD ($) counterparty	Dec. 31, 2023 USD ($) counterparty
Cash and Cash Equivalents
Concentration Risk [Line Items]
Amount of Exposure \| $	$ 187,467	$ 228,927
Number of Counterparties with Exposure \| counterparty	11	11
Percentage of Total Outstanding Unpaid Principal Balance	49.60%	28.80%
Collateral On Repurchase Agreements Held By Dealers
Concentration Risk [Line Items]
Amount of Exposure \| $	$ 3,122,176	$ 3,672,278
Number of Counterparties with Exposure \| counterparty	27	28
Percentage of Total Outstanding Unpaid Principal Balance	26.20%	18.60%
Due From Broker
Concentration Risk [Line Items]
Amount of Exposure \| $	$ 17,099	$ 51,884
Number of Counterparties with Exposure \| counterparty	23	21
Percentage of Total Outstanding Unpaid Principal Balance	41.00%	58.50%
Receivable For Securities Sold
Concentration Risk [Line Items]
Amount of Exposure \| $	$ 14,598	$ 345,429
Number of Counterparties with Exposure \| counterparty	6	9
Percentage of Total Outstanding Unpaid Principal Balance	40.00%	54.30%

Concentration Risk, Number Of Counterparties With Concentration Risk Exposure

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- Definition

Maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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