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Investment Securities - Amortized Cost and Fair Value of Available-for-Sale Investment Securities Portfolio (Details) - USD ($) $ in Thousands | Sep. 30, 2024 | Dec. 31, 2023
--- | --- | ---
Available-for-Sale |  |
Total | $ 8,233,232 | $ 7,684,889
Unrealized Gains | 22,804 | 4,607
Unrealized Losses | (737,752) | (874,143)
Basis adjustments | (85,844) | (102,298)
Fair Value | 7,432,440 | 6,713,055
U.S. Treasury |  |
Available-for-Sale |  |
Total | 260,893 | 449,817
Unrealized Gains | 157 | 154
Unrealized Losses | (13,076) | (11,941)
Basis adjustments | (37,696) | (41,297)
Fair Value | 210,278 | 396,733
U.S. government-sponsored entities and agencies |  |
Available-for-Sale |  |
Total | 1,506,552 | 1,487,879
Unrealized Gains | 227 | 33
Unrealized Losses | (160,832) | (192,717)
Basis adjustments | (51,669) | (63,931)
Fair Value | 1,294,278 | 1,231,264
Mortgage-backed securities |  |
Available-for-Sale |  |
Total | 5,608,308 | 4,835,319
Unrealized Gains | 20,435 | 3,093
Unrealized Losses | (527,687) | (621,852)
Basis adjustments | 0 | 0
Fair Value | 5,101,056 | 4,216,560
States and political subdivisions |  |
Available-for-Sale |  |
Total | 527,887 | 554,509
Unrealized Gains | 1,199 | 878
Unrealized Losses | (21,042) | (23,057)
Basis adjustments | 3,521 | 2,930
Fair Value | 511,565 | 535,260
Pooled trust preferred securities |  |
Available-for-Sale |  |
Total | 13,805 | 13,797
Unrealized Gains | 0 | 0
Unrealized Losses | (2,648) | (2,460)
Basis adjustments | 0 | 0
Fair Value | 11,157 | 11,337
Other securities |  |
Available-for-Sale |  |
Total | 315,787 | 343,568
Unrealized Gains | 786 | 449
Unrealized Losses | (12,467) | (22,116)
Basis adjustments | 0 | 0
Fair Value | $ 304,106 | $ 321,901

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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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