v3.26.3
Derivative and Credit Risk Transfer Strip Assets and Liabilities - Summary of Derivative Liabilities, Financial Liabilities and Collateral Pledged by Counterparty (Detail) - Unpaid Principal Balance Before Unamortized Debt Issuance Costs Adjustment [Member] - USD ($)
$ in Thousands
Sep. 30, 2026
Dec. 31, 2025
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet $ 8,389,894 $ 8,024,089
Gross amounts not offset in the consolidated balance sheet, Financial instruments (8,383,792) (8,023,156)
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 6,102 933
Bank of America, N.A. [Member] | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 1,465,715 1,074,334
Gross amounts not offset in the consolidated balance sheet, Financial instruments (1,465,715) (1,074,334)
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 0 0
Santander US Capital [Member] | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 1,346,450 952,951
Gross amounts not offset in the consolidated balance sheet, Financial instruments (1,346,450) (952,933)
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 0 18
J.P. Morgan Securities LLC [Member] | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 988,161 1,536,038
Gross amounts not offset in the consolidated balance sheet, Financial instruments (988,161) (1,536,038)
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 0 0
Wells Fargo Securities L L C | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 814,970 782,547
Gross amounts not offset in the consolidated balance sheet, Financial instruments (814,499) (782,547)
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 471 0
Atlas Securitized Products, L.P. [Member] | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 709,399 1,216,779
Gross amounts not offset in the consolidated balance sheet, Financial instruments (709,399) (1,216,779)
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 0 0
Citigroup Global Markets Inc. [Member] | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 562,910 397,162
Gross amounts not offset in the consolidated balance sheet, Financial instruments (562,667) (397,162)
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 243 0
Barclays Capital Inc. [Member] | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 470,168 431,016
Gross amounts not offset in the consolidated balance sheet, Financial instruments (468,959) (431,016)
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 1,209 0
Morgan Stanley & Co. LLC [Member] | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 442,352 319,500
Gross amounts not offset in the consolidated balance sheet, Financial instruments (439,804) (319,500)
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 2,548 0
Nomura Holdings America, Inc [Member] | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 394,628 231,308
Gross amounts not offset in the consolidated balance sheet, Financial instruments (394,628) (231,308)
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 0 0
Bank of Montreal [Member] | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 358,433 160,388
Gross amounts not offset in the consolidated balance sheet, Financial instruments (358,267) (160,324)
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 166 64
RBC Capital Markets, L.P. [Member] | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 243,687 438,781
Gross amounts not offset in the consolidated balance sheet, Financial instruments (243,687) (438,781)
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 0 0
BNP Paribas [Member] | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 196,344 54,191
Gross amounts not offset in the consolidated balance sheet, Financial instruments (196,344) (54,191)
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 0 0
Daiwa Capital Markets [Member] | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 168,993 195,268
Gross amounts not offset in the consolidated balance sheet, Financial instruments (168,921) (195,268)
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 72 0
Goldman Sachs & Co. LLC [Member] | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 164,011 151,274
Gross amounts not offset in the consolidated balance sheet, Financial instruments (163,491) (151,274)
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 520 0
Mizuho Financial Group [Member] | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 63,108 81,701
Gross amounts not offset in the consolidated balance sheet, Financial instruments (62,800) (81,701)
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 308 0
Other [Member] | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 565 851
Gross amounts not offset in the consolidated balance sheet, Financial instruments 0 0
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount 565 851
PennyMac Financial Services, Inc. [Member] | Security Sold Under Agreements to Repurchase [Member]    
Offsetting Liabilities [Line Items]    
Net amount of liabilities presented in the consolidated balance sheet 16,456 2,257
Gross amounts not offset in the consolidated balance sheet, Financial instruments 0 0
Gross amounts not offset in the consolidated balance sheet, Cash collateral pledged 0 0
Net amount $ 16,456 $ 2,257