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Investment Securities Available for Sale, at Fair Value - Narrative (Details) - USD ($) | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2021 | Dec. 31, 2020
Schedule of Investments [Line Items] |  |
Interest receivable | $ 1,000,000 | $ 2,400,000
Contractual maturities (up to) | 38 years |
Weighted average life of available for sale securities portfolio | 5 years 4 months 24 days | 5 years 7 months 6 days
Allowance for credit loss | $ 0 | $ 0
Gross unrealized losses | (440,000) | $ (5,374,000)
Non-Agency RMBS And CMBS |  |
Schedule of Investments [Line Items] |  |
Gross unrealized losses | $ (400,000) |

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- Definition Amount excluding accrued interest, of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454 + Details
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