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Investment Securities - Amortized Cost and Fair Value of Available-for-Sale Investment Securities Portfolio (Details) - USD ($) $ in Thousands | Mar. 31, 2025 | Dec. 31, 2024
--- | --- | ---
Available-for-Sale |  |
Total | $ 8,643,126 | $ 8,480,508
Unrealized Gains | 20,152 | 6,987
Unrealized Losses | (796,933) | (897,516)
Basis adjustments | (112,374) | (131,520)
Fair Value | 7,753,971 | 7,458,459
U.S. Treasury |  |
Available-for-Sale |  |
Total | 261,345 | 261,421
Unrealized Gains | 87 | 67
Unrealized Losses | (10,931) | (12,659)
Basis adjustments | (45,964) | (49,816)
Fair Value | 204,537 | 199,013
U.S. government-sponsored entities and agencies |  |
Available-for-Sale |  |
Total | 1,554,502 | 1,521,610
Unrealized Gains | 238 | 7
Unrealized Losses | (161,684) | (181,360)
Basis adjustments | (68,253) | (82,351)
Fair Value | 1,324,803 | 1,257,906
Mortgage-backed securities |  |
Available-for-Sale |  |
Total | 6,064,171 | 5,861,067
Unrealized Gains | 18,649 | 6,005
Unrealized Losses | (582,801) | (662,181)
Basis adjustments | 0 | 0
Fair Value | 5,500,019 | 5,204,891
States and political subdivisions |  |
Available-for-Sale |  |
Total | 466,473 | 510,630
Unrealized Gains | 213 | 148
Unrealized Losses | (29,073) | (25,881)
Basis adjustments | 1,843 | 647
Fair Value | 439,456 | 485,544
Pooled trust preferred securities |  |
Available-for-Sale |  |
Total | 13,809 | 13,807
Unrealized Gains | 0 | 0
Unrealized Losses | (2,498) | (2,485)
Basis adjustments | 0 | 0
Fair Value | 11,311 | 11,322
Other securities |  |
Available-for-Sale |  |
Total | 282,826 | 311,973
Unrealized Gains | 965 | 760
Unrealized Losses | (9,946) | (12,950)
Basis adjustments | 0 | 0
Fair Value | $ 273,845 | $ 299,783

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- Definition Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-2 + Details
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