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Investment Securities - Available-for-Sale and Held-to-Maturity Investment Securities with Unrealized Losses by Aggregated Major Security Type and Length of Time in Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024
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Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items] |  |
Available-for-Sale, Less than 12 months, Fair Value | $ 408,709 | $ 1,126,895
Available-for-Sale, Less than 12 months, Unrealized Losses | (2,330) | (12,668)
Available-for-Sale, 12 months or longer, Fair Value | 4,994,715 | 5,218,733
Available-for-Sale, 12 months or longer, Unrealized Losses | (697,382) | (884,848)
Available-for-Sale, Fair Value | 5,403,424 | 6,345,628
Available-for-Sale, Unrealized Losses | (699,712) | (897,516)
U.S. Treasury |  |
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items] |  |
Available-for-Sale, Less than 12 months, Fair Value | 998 | 3,977
Available-for-Sale, Less than 12 months, Unrealized Losses | 0 | (26)
Available-for-Sale, 12 months or longer, Fair Value | 184,848 | 177,691
Available-for-Sale, 12 months or longer, Unrealized Losses | (10,230) | (12,633)
Available-for-Sale, Fair Value | 185,846 | 181,668
Available-for-Sale, Unrealized Losses | (10,230) | (12,659)
U.S. government-sponsored entities and agencies |  |
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items] |  |
Available-for-Sale, Less than 12 months, Fair Value | 84,581 | 98,280
Available-for-Sale, Less than 12 months, Unrealized Losses | (413) | (1,713)
Available-for-Sale, 12 months or longer, Fair Value | 1,165,864 | 1,144,618
Available-for-Sale, 12 months or longer, Unrealized Losses | (146,112) | (179,647)
Available-for-Sale, Fair Value | 1,250,445 | 1,242,898
Available-for-Sale, Unrealized Losses | (146,525) | (181,360)
Mortgage-backed securities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items] |  |
Available-for-Sale, Less than 12 months, Fair Value | 296,110 | 857,440
Available-for-Sale, Less than 12 months, Unrealized Losses | (1,726) | (9,172)
Available-for-Sale, 12 months or longer, Fair Value | 3,247,585 | 3,406,350
Available-for-Sale, 12 months or longer, Unrealized Losses | (510,901) | (653,009)
Available-for-Sale, Fair Value | 3,543,695 | 4,263,790
Available-for-Sale, Unrealized Losses | (512,627) | (662,181)
States and political subdivisions |  |
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items] |  |
Available-for-Sale, Less than 12 months, Fair Value | 9,884 | 133,906
Available-for-Sale, Less than 12 months, Unrealized Losses | (65) | (1,462)
Available-for-Sale, 12 months or longer, Fair Value | 240,834 | 279,121
Available-for-Sale, 12 months or longer, Unrealized Losses | (21,617) | (24,419)
Available-for-Sale, Fair Value | 250,718 | 413,027
Available-for-Sale, Unrealized Losses | (21,682) | (25,881)
Pooled trust preferred securities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items] |  |
Available-for-Sale, Less than 12 months, Fair Value | 0 | 0
Available-for-Sale, Less than 12 months, Unrealized Losses | 0 | 0
Available-for-Sale, 12 months or longer, Fair Value | 11,533 | 11,322
Available-for-Sale, 12 months or longer, Unrealized Losses | (2,283) | (2,485)
Available-for-Sale, Fair Value | 11,533 | 11,322
Available-for-Sale, Unrealized Losses | (2,283) | (2,485)
Other securities |  |
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items] |  |
Available-for-Sale, Less than 12 months, Fair Value | 17,136 | 33,292
Available-for-Sale, Less than 12 months, Unrealized Losses | (126) | (295)
Available-for-Sale, 12 months or longer, Fair Value | 144,051 | 199,631
Available-for-Sale, 12 months or longer, Unrealized Losses | (6,239) | (12,655)
Available-for-Sale, Fair Value | 161,187 | 232,923
Available-for-Sale, Unrealized Losses | $ (6,365) | $ (12,950)

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