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Summary of Significant Accounting Policies - Additional Information (Detail)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2020
shares
Sep. 30, 2019
shares
Sep. 30, 2020
shares
Sep. 30, 2019
shares
Nov. 05, 2020
USD ($)
Deferral
Borrower
Summary Of Significant Accounting Policies [Line Items]          
Dilutive common shares outstanding | shares 0 0 0 0  
Subsequent Event [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Number of executed deferrals on outstanding loan balances as per interagency | Deferral         553
Executed deferrals on outstanding Loan balance as per interagency         $ 109.9
Percentage of held-for-investment loan portfolio         16.40%
Number of borrowers | Borrower         5
Deferred loan balance         $ 6.5