v3.26.1
Fair Value - Quantitative Summary of Key Unobservable Inputs Used in Review and Approval of Broker-provided Fair Values for CRT Derivatives (Detail) - CRT Derivatives [Member] - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2026
Dec. 31, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value $ 30,174 $ 32,659
UPB of loans in reference pools $ 4,046,852 $ 4,555,682
Discount Rate [Member] | Minimum [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Key inputs used in fair value for CRT agreements 8.80% 8.60%
Discount Rate [Member] | Maximum [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Key inputs used in fair value for CRT agreements 10.10% 14.10%
Discount Rate [Member] | Weighted Average [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Key inputs used in fair value for CRT agreements 8.80% 8.80%
Voluntary Prepayment Speed [Member] | Minimum [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Key inputs used in fair value for CRT agreements 7.40% 6.30%
Voluntary Prepayment Speed [Member] | Maximum [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Key inputs used in fair value for CRT agreements 8.30% 7.60%
Voluntary Prepayment Speed [Member] | Weighted Average [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Key inputs used in fair value for CRT agreements 7.60% 7.30%
Involuntary Prepayment Speed [Member] | Minimum [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Key inputs used in fair value for CRT agreements 0.20% 0.10%
Involuntary Prepayment Speed [Member] | Maximum [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Key inputs used in fair value for CRT agreements 0.20% 0.30%
Involuntary Prepayment Speed [Member] | Weighted Average [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Key inputs used in fair value for CRT agreements 0.20% 0.10%
Measurement Input, Loss Severity | Minimum [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Key inputs used in fair value for CRT agreements 0.00% 0.00%
Measurement Input, Loss Severity | Maximum [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Key inputs used in fair value for CRT agreements 0.10% 0.10%
Measurement Input, Loss Severity | Weighted Average [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Key inputs used in fair value for CRT agreements 0.10% 0.10%