Investment Securities - Schedule of Securities With Unrealized Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	$ 11,311	$ 37,952
Available-for-sale, less than 12 months, gross unrealized losses	(1,069)	(411)
Available-for-sale, 12 months or more, estimated fair value	2,680,405	2,429,271
Available-for-sale, 12 months or more, gross unrealized losses	(408,879)	(323,244)
Available-for-sale, total, estimated fair value	2,691,716	2,467,223
Available-for-sale, total, gross unrealized losses	(409,948)	(323,655)
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value		0
Available-for-sale, less than 12 months, gross unrealized losses		0
Available-for-sale, 12 months or more, estimated fair value		996
Available-for-sale, 12 months or more, gross unrealized losses		(3)
Available-for-sale, total, estimated fair value		996
Available-for-sale, total, gross unrealized losses		(3)
U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	2,301	717
Available-for-sale, less than 12 months, gross unrealized losses	(23)	(7)
Available-for-sale, 12 months or more, estimated fair value	44,694	51,186
Available-for-sale, 12 months or more, gross unrealized losses	(676)	(1,040)
Available-for-sale, total, estimated fair value	46,995	51,903
Available-for-sale, total, gross unrealized losses	(699)	(1,047)
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	3,255	7,480
Available-for-sale, less than 12 months, gross unrealized losses	(18)	(189)
Available-for-sale, 12 months or more, estimated fair value	1,718,920	1,384,532
Available-for-sale, 12 months or more, gross unrealized losses	(202,132)	(152,595)
Available-for-sale, total, estimated fair value	1,722,175	1,392,012
Available-for-sale, total, gross unrealized losses	(202,150)	(152,784)
State and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	5,755	16,843
Available-for-sale, less than 12 months, gross unrealized losses	(1,028)	(195)
Available-for-sale, 12 months or more, estimated fair value	811,631	829,754
Available-for-sale, 12 months or more, gross unrealized losses	(199,339)	(157,374)
Available-for-sale, total, estimated fair value	817,386	846,597
Available-for-sale, total, gross unrealized losses	(200,367)	(157,569)
Other securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	0	12,912
Available-for-sale, less than 12 months, gross unrealized losses	0	(20)
Available-for-sale, 12 months or more, estimated fair value	105,160	162,803
Available-for-sale, 12 months or more, gross unrealized losses	(6,732)	(12,232)
Available-for-sale, total, estimated fair value	105,160	175,715
Available-for-sale, total, gross unrealized losses	$ (6,732)	$ (12,252)