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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) - Reverse Mortgage Loans Held for Investment, Subject to HMBS Related Obligations [Member]
6 Months Ended 12 Months Ended
Jun. 30, 2022
Dec. 31, 2021
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 23.00% 20.80%
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 3.90% 4.50%
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 2.40% 3.10%
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 6.90% 7.70%
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 2.60% 3.30%
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 4.20% 2.40%
Average draw rate 1.20% 1.10%