Note 2 - Mortgage-backed Securities and U.S. Treasury Securities, At Fair Value - Schedule of RMBS Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Mortgage-backed securities	$ 4,520,225	$ 3,540,002
Pass Through Certificate [Member]
Mortgage-backed securities	4,502,115	3,519,906
Pass Through Certificate [Member] \| Fixed Rate Mortgages [Member]
Mortgage-backed securities	4,502,115	3,519,906
Structured Finance [Member]
Mortgage-backed securities	18,110	20,096
Structured Finance [Member] \| Interest Only Securities [Member]
Mortgage-backed securities	17,833	19,669
Structured Finance [Member] \| Inverse Interest Only Securities [Member]
Mortgage-backed securities	$ 277	$ 427

The fair value as of the balance sheet date of firm holdings in mortgages, mortgage backed securities (investment instruments that represent ownership of an undivided interest in a group of mortgages, where principal and interest from the individual mortgages are used to pay investors' principal and interest on the mortgage backed security) and asset-backed securities that are primarily paid from the cash flows of a discrete pool of receivables or other financial assets (such as credit-card receivables), either fixed or revolving, that by their terms convert into cash within a finite time period. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 940
-SubTopic 320
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481961/940-320-45-2

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