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Investment Securities - Schedule of Securities With Unrealized Losses (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024
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Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale, less than 12 months, estimated fair value | $ 11,311 | $ 37,952
Available-for-sale, less than 12 months, gross unrealized losses | (1,069) | (411)
Available-for-sale, 12 months or more, estimated fair value | 2,680,405 | 2,429,271
Available-for-sale, 12 months or more, gross unrealized losses | (408,879) | (323,244)
Available-for-sale, total, estimated fair value | 2,691,716 | 2,467,223
Available-for-sale, total, gross unrealized losses | (409,948) | (323,655)
U.S. Treasury |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale, less than 12 months, estimated fair value |  | 0
Available-for-sale, less than 12 months, gross unrealized losses |  | 0
Available-for-sale, 12 months or more, estimated fair value |  | 996
Available-for-sale, 12 months or more, gross unrealized losses |  | (3)
Available-for-sale, total, estimated fair value |  | 996
Available-for-sale, total, gross unrealized losses |  | (3)
U.S. Government agencies |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale, less than 12 months, estimated fair value | 2,301 | 717
Available-for-sale, less than 12 months, gross unrealized losses | (23) | (7)
Available-for-sale, 12 months or more, estimated fair value | 44,694 | 51,186
Available-for-sale, 12 months or more, gross unrealized losses | (676) | (1,040)
Available-for-sale, total, estimated fair value | 46,995 | 51,903
Available-for-sale, total, gross unrealized losses | (699) | (1,047)
Mortgage-backed securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale, less than 12 months, estimated fair value | 3,255 | 7,480
Available-for-sale, less than 12 months, gross unrealized losses | (18) | (189)
Available-for-sale, 12 months or more, estimated fair value | 1,718,920 | 1,384,532
Available-for-sale, 12 months or more, gross unrealized losses | (202,132) | (152,595)
Available-for-sale, total, estimated fair value | 1,722,175 | 1,392,012
Available-for-sale, total, gross unrealized losses | (202,150) | (152,784)
State and political subdivisions |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale, less than 12 months, estimated fair value | 5,755 | 16,843
Available-for-sale, less than 12 months, gross unrealized losses | (1,028) | (195)
Available-for-sale, 12 months or more, estimated fair value | 811,631 | 829,754
Available-for-sale, 12 months or more, gross unrealized losses | (199,339) | (157,374)
Available-for-sale, total, estimated fair value | 817,386 | 846,597
Available-for-sale, total, gross unrealized losses | (200,367) | (157,569)
Other securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale, less than 12 months, estimated fair value | 0 | 12,912
Available-for-sale, less than 12 months, gross unrealized losses | 0 | (20)
Available-for-sale, 12 months or more, estimated fair value | 105,160 | 162,803
Available-for-sale, 12 months or more, gross unrealized losses | (6,732) | (12,232)
Available-for-sale, total, estimated fair value | 105,160 | 175,715
Available-for-sale, total, gross unrealized losses | $ (6,732) | $ (12,252)

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