Investment Securities - Schedule of Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Available-for-Sale:
Available-for-Sale: Amortized Cost	$ 2,585,893	$ 2,694,012
Available-for-Sale: Gross Unrealized Gains	643	704
Available-for-Sale: Gross Unrealized Losses	(288,444)	(285,783)
Available-for-Sale: Fair Value	2,298,092	2,408,933
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	4,812,954	4,997,335
Held-to-Maturity: Gross Unrealized Gains	25	29
Held-to-Maturity: Gross Unrealized Losses	(810,857)	(743,727)
Held-to-Maturity: Fair Value	4,002,122	4,253,637
Debt Securities Issued by the U.S. Treasury and Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	212,413	223,308
Available-for-Sale: Gross Unrealized Gains	320	361
Available-for-Sale: Gross Unrealized Losses	(10,979)	(11,096)
Available-for-Sale: Fair Value	201,754	212,573
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	131,805	131,742
Held-to-Maturity: Gross Unrealized Losses	(16,602)	(15,211)
Held-to-Maturity: Fair Value	115,203	116,531
Debt Securities Issued by States and Political Subdivisions
Available-for-Sale:
Available-for-Sale: Amortized Cost	73,292	73,417
Available-for-Sale: Gross Unrealized Losses	(10,146)	(9,611)
Available-for-Sale: Fair Value	63,146	63,806
Debt Securities Issued by Government-Sponsored Enterprises
Available-for-Sale:
Available-for-Sale: Amortized Cost	1,506	1,556
Available-for-Sale: Gross Unrealized Losses	(74)	(80)
Available-for-Sale: Fair Value	1,432	1,476
Debt Securities Issued by Corporations
Available-for-Sale:
Available-for-Sale: Amortized Cost	704,610	706,002
Available-for-Sale: Gross Unrealized Gains	207	142
Available-for-Sale: Gross Unrealized Losses	(42,193)	(48,443)
Available-for-Sale: Fair Value	662,624	657,701
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	10,867	11,483
Held-to-Maturity: Gross Unrealized Losses	(2,149)	(1,998)
Held-to-Maturity: Fair Value	8,718	9,485
Residential - Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	666,354	713,918
Available-for-Sale: Gross Unrealized Gains	111	194
Available-for-Sale: Gross Unrealized Losses	(87,536)	(84,785)
Available-for-Sale: Fair Value	578,929	629,327
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	1,595,881	1,674,076
Held-to-Maturity: Gross Unrealized Gains	16	20
Held-to-Maturity: Gross Unrealized Losses	(277,950)	(265,493)
Held-to-Maturity: Fair Value	1,317,947	1,408,603
Residential - U.S. Government-Sponsored Enterprises
Available-for-Sale:
Available-for-Sale: Amortized Cost	773,094	818,296
Available-for-Sale: Gross Unrealized Gains	5	7
Available-for-Sale: Gross Unrealized Losses	(113,153)	(109,176)
Available-for-Sale: Fair Value	659,946	709,127
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	2,643,443	2,744,094
Held-to-Maturity: Gross Unrealized Gains	9	9
Held-to-Maturity: Gross Unrealized Losses	(419,247)	(369,965)
Held-to-Maturity: Fair Value	2,224,205	2,374,138
Commercial - Government Agencies or Sponsored Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	154,624	157,515
Available-for-Sale: Gross Unrealized Losses	(24,363)	(22,592)
Available-for-Sale: Fair Value	130,261	134,923
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	430,958	435,940
Held-to-Maturity: Gross Unrealized Losses	(94,909)	(91,060)
Held-to-Maturity: Fair Value	336,049	344,880
Mortgage-Backed Securities
Available-for-Sale:
Available-for-Sale: Amortized Cost	1,594,072	1,689,729
Available-for-Sale: Gross Unrealized Gains	116	201
Available-for-Sale: Gross Unrealized Losses	(225,052)	(216,553)
Available-for-Sale: Fair Value	1,369,136	1,473,377
Held-to-Maturity:
Held-to-Maturity: Amortized Cost	4,670,282	4,854,110
Held-to-Maturity: Gross Unrealized Gains	25	29
Held-to-Maturity: Gross Unrealized Losses	(792,106)	(726,518)
Held-to-Maturity: Fair Value	$ 3,878,201	$ 4,127,621

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).

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Amount, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

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