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Investment Securities Available for Sale, at Fair Value - Narrative (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2021 | Dec. 31, 2020
Schedule of Investments [Line Items] |  |
Interest receivable | $ 2,100,000 | $ 2,400,000
Contractual maturities (up to) | 39 years |
Weighted average life of available for sale securities portfolio | 6 years | 5 years 7 months 6 days
Allowance for credit loss | $ 0 |
Gross unrealized losses | (1,264,000) | $ (5,374,000)
Non-Agency RMBS |  |
Schedule of Investments [Line Items] |  |
Gross unrealized losses | (867,000) | $ (5,374,000)
CMBS |  |
Schedule of Investments [Line Items] |  |
Gross unrealized losses | $ (397,000) |

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