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Mortgage-Backed and Credit Risk Transfer Securities - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]      
Allowance for credit losses $ 0 $ 1,768,000 $ 0
Additional increases or decreases in the allowance for credit losses on securities that had an allowance recorded in a previous period $ (1,768,000) 0  
Impairment of non-agency securities   94,100,000  
Non-Agency CMBS      
Debt Securities, Available-for-sale [Line Items]      
Allowance for credit losses   $ 1,768,000