Annual report pursuant to Section 13 and 15(d)

Fair Value - Summary of Reverse Mortgage Loans Held for Investment, Subject to HMBS Related Obligations (Detail)

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Fair Value - Summary of Reverse Mortgage Loans Held for Investment, Subject to HMBS Related Obligations (Detail)
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Reverse Mortgage Loans Held for Investment, Subject to HMBS Related Obligations [Member] | Conditional repayment rate [Member] | Weighted Average [Member]    
Fair Value Reverse Mortgage Loans Held For Investment Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Conditional repayment rate 20.80% 20.00%
Reverse Mortgage Loans Held for Investment, Subject to HMBS Related Obligations [Member] | Loss frequency [Member] | Weighted Average [Member]    
Fair Value Reverse Mortgage Loans Held For Investment Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Loss frequency 4.50% 4.40%
Reverse Mortgage Loans Held for Investment, Subject to HMBS Related Obligations [Member] | Loss severity [Member] | Minimum [Member]    
Fair Value Reverse Mortgage Loans Held For Investment Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Loss severity 3.10% 5.10%
Reverse Mortgage Loans Held for Investment, Subject to HMBS Related Obligations [Member] | Loss severity [Member] | Maximum [Member]    
Fair Value Reverse Mortgage Loans Held For Investment Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Loss severity 7.70% 13.30%
Reverse Mortgage Loans Held for Investment, Subject to HMBS Related Obligations [Member] | Loss severity [Member] | Weighted Average [Member]    
Fair Value Reverse Mortgage Loans Held For Investment Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Loss severity 3.30% 5.40%
Reverse Mortgage Loans Held for Investment, Subject to HMBS Related Obligations [Member] | Discount rate [Member] | Weighted Average [Member]    
Fair Value Reverse Mortgage Loans Held For Investment Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Discount rate 2.40% 1.60%
Average draw rate 1.10% 1.10%
HMBS Related Obligations At Fair Value [Member] | Conditional repayment rate [Member] | Weighted Average [Member]    
Fair Value Reverse Mortgage Loans Held For Investment Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Conditional repayment rate 20.80% 19.90%
HMBS Related Obligations At Fair Value [Member] | Discount rate [Member] | Weighted Average [Member]    
Fair Value Reverse Mortgage Loans Held For Investment Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Discount rate 2.30% 1.40%