Quarterly report pursuant to Section 13 or 15(d)

Fair Value - Summary of HMBS Related Obligations (Detail)

v3.21.2
Fair Value - Summary of HMBS Related Obligations (Detail) - HMBS Related Obligations [Member] - Weighted Average [Member]
 9 Months Ended 12 Months Ended
Sep. 30, 2021
Dec. 31, 2020
Conditional repayment rate [Member]    
Fair Value HMBS Related Obligations Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Conditional repayment rate 20.90% 19.90%
Discount rate [Member]    
Fair Value HMBS Related Obligations Measured On Recurring And Nonrecurring Basis Fair Value Measurement [Line Items]    
Discount rate 2.10% 1.40%