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

Debt Securities, Available-For-Sale, Accumulated Basis Adjustments, Before Tax

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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

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Amount, before tax, of unrealized loss 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 (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

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Amortized cost excluding accrued interest, before allowance for credit loss, of 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 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479130/326-30-45-1

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- Definition

Amount excluding accrued interest, of 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/2009/role/commonPracticeRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479130/326-30-45-1

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