Mortgage-Backed Securities - Summary of Investment in Mortgage Backed Securities Activity (Detail) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
Sep. 30, 2026 |
Sep. 30, 2025 |
|
| Mortgage Backed Securities [Line Items] | ||||
| Balance at beginning of period | $ 4,452,859 | |||
| Changes in fair value included in income arising from: | ||||
| Balance at end of period | $ 4,305,991 | 4,305,991 | ||
| Mortgage Backed Securities [Member] | ||||
| Mortgage Backed Securities [Line Items] | ||||
| Balance at beginning of period | 4,075,660 | $ 3,967,045 | 4,452,859 | $ 4,063,706 |
| Purchases | 548,174 | 905,380 | 1,038,581 | 942,462 |
| Sales | 0 | (194,513) | (477,360) | (194,513) |
| Repayments | (135,259) | (126,857) | (510,528) | (357,671) |
| Changes in fair value included in income arising from: | ||||
| Amortization and accrual of net purchase premiums and discounts , net | (15,637) | 20,537 | 2,367 | 38,189 |
| Valuation adjustments, net | (166,947) | 37,572 | (199,928) | 116,991 |
| Total changes in fair value included in income | (182,584) | 58,109 | (197,561) | 155,180 |
| Balance at end of period | $ 4,305,991 | $ 4,609,164 | $ 4,305,991 | $ 4,609,164 |