Quarterly report pursuant to Section 13 or 15(d)

Fair Value - Summary of Non-Agency Reverse Mortgage Securitized (Detail)

v3.21.2
Fair Value - Summary of Non-Agency Reverse Mortgage Securitized (Detail) - Non Agency Reverse Mortgage Securitized [Member]
9 Months Ended 12 Months Ended
Sep. 30, 2021
Dec. 31, 2020
Minimum [Member] | Loan to value [Member]    
Fair Value Non Agency Reverse Mortgage Loan Held For Investment Subject To Nonrecourse Debt Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Loan to value 0.10% 9.00%
Minimum [Member] | Home price appreciation [Member]    
Fair Value Non Agency Reverse Mortgage Loan Held For Investment Subject To Nonrecourse Debt Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Home price appreciation 3.40% 1.10%
Maximum [Member] | Loan to value [Member]    
Fair Value Non Agency Reverse Mortgage Loan Held For Investment Subject To Nonrecourse Debt Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Loan to value 63.10% 73.10%
Maximum [Member] | Home price appreciation [Member]    
Fair Value Non Agency Reverse Mortgage Loan Held For Investment Subject To Nonrecourse Debt Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Home price appreciation 9.60% 8.90%
Weighted Average [Member] | Weighted average remaining life in years [Member]    
Fair Value Non Agency Reverse Mortgage Loan Held For Investment Subject To Nonrecourse Debt Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Weighted-average remaining life in years 7 years 2 months 12 days 6 years 10 months 24 days
Weighted Average [Member] | Loan to value [Member]    
Fair Value Non Agency Reverse Mortgage Loan Held For Investment Subject To Nonrecourse Debt Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Loan to value 42.90% 48.20%
Weighted Average [Member] | Conditional repayment rate [Member]    
Fair Value Non Agency Reverse Mortgage Loan Held For Investment Subject To Nonrecourse Debt Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Conditional repayment rate 19.20% 18.70%
Weighted Average [Member] | Loss severity [Member]    
Fair Value Non Agency Reverse Mortgage Loan Held For Investment Subject To Nonrecourse Debt Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Loss severity 10.00% 10.00%
Weighted Average [Member] | Home price appreciation [Member]    
Fair Value Non Agency Reverse Mortgage Loan Held For Investment Subject To Nonrecourse Debt Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Home price appreciation 4.70% 5.60%
Weighted Average [Member] | Discount rate [Member]    
Fair Value Non Agency Reverse Mortgage Loan Held For Investment Subject To Nonrecourse Debt Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Discount rate 3.40% 3.60%