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Investment Securities - Schedule of Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Investment Securities (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Available-for-Sale: |  |
Available-for-Sale: Amortized Cost | $ 3,460,563 | $ 2,947,415
Available-for-Sale: Gross Unrealized Gains | 7,969 | 1,248
Available-for-Sale: Gross Unrealized Losses | (188,122) | (259,135)
Total Investment Securities Available-for-Sale | 3,280,410 | 2,689,528
Held-to-Maturity: |  |
Held-to-Maturity: Amortized Cost | 4,340,032 | 4,618,543
Held-to-Maturity: Gross Unrealized Gains | 332 | 40
Held-to-Maturity: Gross Unrealized Losses | (622,791) | (797,701)
Investment Securities Held-to-Maturity | 3,717,573 | 3,820,882
Debt Securities Issued by the U.S. Treasury and Government Agencies |  |
Available-for-Sale: |  |
Available-for-Sale: Amortized Cost | 245,946 | 257,036
Available-for-Sale: Gross Unrealized Gains | 176 | 221
Available-for-Sale: Gross Unrealized Losses | (4,281) | (8,185)
Total Investment Securities Available-for-Sale | 241,841 | 249,072
Held-to-Maturity: |  |
Held-to-Maturity: Amortized Cost | 129,463 | 131,868
Held-to-Maturity: Gross Unrealized Gains | 0 | 0
Held-to-Maturity: Gross Unrealized Losses | (9,696) | (14,927)
Investment Securities Held-to-Maturity | 119,767 | 116,941
Debt Securities Issued by States and Political Subdivisions |  |
Available-for-Sale: |  |
Available-for-Sale: Amortized Cost | 72,434 | 73,208
Available-for-Sale: Gross Unrealized Gains | 0 | 0
Available-for-Sale: Gross Unrealized Losses | (6,393) | (9,349)
Total Investment Securities Available-for-Sale | 66,041 | 63,859
Debt Securities Issued by U.S. Government-Sponsored Enterprises |  |
Available-for-Sale: |  |
Available-for-Sale: Amortized Cost | 1,004 | 1,505
Available-for-Sale: Gross Unrealized Gains | 0 | 0
Available-for-Sale: Gross Unrealized Losses | (13) | (41)
Total Investment Securities Available-for-Sale | 991 | 1,464
Debt Securities Issued by Corporations |  |
Available-for-Sale: |  |
Available-for-Sale: Amortized Cost | 752,393 | 703,579
Available-for-Sale: Gross Unrealized Gains | 2,011 | 376
Available-for-Sale: Gross Unrealized Losses | (21,477) | (32,280)
Total Investment Securities Available-for-Sale | 732,927 | 671,675
Held-to-Maturity: |  |
Held-to-Maturity: Amortized Cost | 10,286 | 10,490
Held-to-Maturity: Gross Unrealized Gains | 0 | 0
Held-to-Maturity: Gross Unrealized Losses | (1,738) | (2,156)
Investment Securities Held-to-Maturity | 8,548 | 8,334
Total Collateralized Mortgage Obligations |  |
Available-for-Sale: |  |
Available-for-Sale: Amortized Cost | 1,707,390 | 1,356,995
Available-for-Sale: Gross Unrealized Gains | 2,816 | 521
Available-for-Sale: Gross Unrealized Losses | (108,831) | (138,822)
Total Investment Securities Available-for-Sale | 1,601,375 | 1,218,694
Held-to-Maturity: |  |
Held-to-Maturity: Amortized Cost | 2,451,264 | 2,601,599
Held-to-Maturity: Gross Unrealized Gains | 4 | 3
Held-to-Maturity: Gross Unrealized Losses | (371,914) | (469,360)
Investment Securities Held-to-Maturity | 2,079,354 | 2,132,242
Residential - Government Agencies or Sponsored Enterprises |  |
Available-for-Sale: |  |
Available-for-Sale: Amortized Cost | 1,295,644 | 1,050,299
Available-for-Sale: Gross Unrealized Gains | 2,190 | 322
Available-for-Sale: Gross Unrealized Losses | (87,243) | (115,401)
Total Investment Securities Available-for-Sale | 1,210,591 | 935,220
Held-to-Maturity: |  |
Held-to-Maturity: Amortized Cost | 2,041,489 | 2,185,210
Held-to-Maturity: Gross Unrealized Gains | 4 | 3
Held-to-Maturity: Gross Unrealized Losses | (291,372) | (377,149)
Investment Securities Held-to-Maturity | 1,750,121 | 1,808,064
Commercial - Government Agencies or Sponsored Enterprises |  |
Available-for-Sale: |  |
Available-for-Sale: Amortized Cost | 351,102 | 306,696
Available-for-Sale: Gross Unrealized Gains | 544 | 199
Available-for-Sale: Gross Unrealized Losses | (21,461) | (23,421)
Total Investment Securities Available-for-Sale | 330,185 | 283,474
Held-to-Maturity: |  |
Held-to-Maturity: Amortized Cost | 409,775 | 416,389
Held-to-Maturity: Gross Unrealized Gains | 0 | 0
Held-to-Maturity: Gross Unrealized Losses | (80,542) | (92,211)
Investment Securities Held-to-Maturity | 329,233 | 324,178
Commercial - Non-Agency |  |
Available-for-Sale: |  |
Available-for-Sale: Amortized Cost | 60,644 |
Available-for-Sale: Gross Unrealized Gains | 82 |
Available-for-Sale: Gross Unrealized Losses | (127) |
Total Investment Securities Available-for-Sale | 60,599 |
Total Mortgage-Backed Securities |  |
Available-for-Sale: |  |
Available-for-Sale: Amortized Cost | 681,396 | 555,092
Available-for-Sale: Gross Unrealized Gains | 2,966 | 130
Available-for-Sale: Gross Unrealized Losses | (47,127) | (70,458)
Total Investment Securities Available-for-Sale | 637,235 | 484,764
Held-to-Maturity: |  |
Held-to-Maturity: Amortized Cost | 1,749,019 | 1,874,586
Held-to-Maturity: Gross Unrealized Gains | 328 | 37
Held-to-Maturity: Gross Unrealized Losses | (239,443) | (311,258)
Investment Securities Held-to-Maturity | 1,509,904 | 1,563,365
Residential - Government Agencies or Sponsored Agencies |  |
Available-for-Sale: |  |
Available-for-Sale: Amortized Cost | 681,396 | 555,092
Available-for-Sale: Gross Unrealized Gains | 2,966 | 130
Available-for-Sale: Gross Unrealized Losses | (47,127) | (70,458)
Total Investment Securities Available-for-Sale | 637,235 | 484,764
Held-to-Maturity: |  |
Held-to-Maturity: Amortized Cost | 1,739,033 | 1,864,591
Held-to-Maturity: Gross Unrealized Gains | 328 | 37
Held-to-Maturity: Gross Unrealized Losses | (237,717) | (309,093)
Investment Securities Held-to-Maturity | 1,501,644 | 1,555,535
Commercial - Government Agencies or Sponsored Enterprises |  |
Held-to-Maturity: |  |
Held-to-Maturity: Amortized Cost | 9,986 | 9,995
Held-to-Maturity: Gross Unrealized Gains | 0 | 0
Held-to-Maturity: Gross Unrealized Losses | (1,726) | (2,165)
Investment Securities Held-to-Maturity | $ 8,260 | $ 7,830

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