Investment Securities - Securities With Unrealized Losses (Details) $ in Thousands	Sep. 30, 2024 USD ($)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	$ 16,650
Available-for-sale, less than 12 months, gross unrealized losses	(194)
Available-for-sale, 12 months or more, estimated fair value	2,596,857
Available-for-sale, 12 months or more, gross unrealized losses	(285,903)
Available-for-sale, total, estimated fair value	2,613,507
Available-for-sale, total, gross unrealized losses	(286,097)
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	1,290
Available-for-sale, less than 12 months, gross unrealized losses	(7)
Available-for-sale, 12 months or more, estimated fair value	0
Available-for-sale, 12 months or more, gross unrealized losses	0
Available-for-sale, total, estimated fair value	1,290
Available-for-sale, total, gross unrealized losses	(7)
U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	982
Available-for-sale, less than 12 months, gross unrealized losses	(1)
Available-for-sale, 12 months or more, estimated fair value	54,494
Available-for-sale, 12 months or more, gross unrealized losses	(872)
Available-for-sale, total, estimated fair value	55,476
Available-for-sale, total, gross unrealized losses	(873)
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	1,574
Available-for-sale, less than 12 months, gross unrealized losses	(110)
Available-for-sale, 12 months or more, estimated fair value	1,507,414
Available-for-sale, 12 months or more, gross unrealized losses	(123,897)
Available-for-sale, total, estimated fair value	1,508,988
Available-for-sale, total, gross unrealized losses	(124,007)
State and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	4,934
Available-for-sale, less than 12 months, gross unrealized losses	(17)
Available-for-sale, 12 months or more, estimated fair value	867,223
Available-for-sale, 12 months or more, gross unrealized losses	(144,808)
Available-for-sale, total, estimated fair value	872,157
Available-for-sale, total, gross unrealized losses	(144,825)
Other securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	7,870
Available-for-sale, less than 12 months, gross unrealized losses	(59)
Available-for-sale, 12 months or more, estimated fair value	167,726
Available-for-sale, 12 months or more, gross unrealized losses	(16,326)
Available-for-sale, total, estimated fair value	175,596
Available-for-sale, total, gross unrealized losses	$ (16,385)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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