Investment Securities - Securities With Unrealized Losses (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Available-for-sale
Available-for-sale, less than 12 months, estimated fair value	$ 37,952	$ 31,862
Available-for-sale, less than 12 months, gross unrealized losses	(411)	(2,991)
Available-for-sale, 12 months or more, estimated fair value	2,429,271	3,084,495
Available-for-sale, 12 months or more, gross unrealized losses	(323,244)	(354,795)
Available-for-sale, total, estimated fair value	2,467,223	3,116,357
Available-for-sale, total, gross unrealized losses	(323,655)	(357,786)
U.S. Treasury
Available-for-sale
Available-for-sale, less than 12 months, estimated fair value	0	0
Available-for-sale, less than 12 months, gross unrealized losses	0	0
Available-for-sale, 12 months or more, estimated fair value	996	2,254
Available-for-sale, 12 months or more, gross unrealized losses	(3)	(31)
Available-for-sale, total, estimated fair value	996	2,254
Available-for-sale, total, gross unrealized losses	(3)	(31)
U.S. Government agencies
Available-for-sale
Available-for-sale, less than 12 months, estimated fair value	717	8,614
Available-for-sale, less than 12 months, gross unrealized losses	(7)	(39)
Available-for-sale, 12 months or more, estimated fair value	51,186	59,732
Available-for-sale, 12 months or more, gross unrealized losses	(1,040)	(1,954)
Available-for-sale, total, estimated fair value	51,903	68,346
Available-for-sale, total, gross unrealized losses	(1,047)	(1,993)
Mortgage-backed securities
Available-for-sale
Available-for-sale, less than 12 months, estimated fair value	7,480	9,182
Available-for-sale, less than 12 months, gross unrealized losses	(189)	(135)
Available-for-sale, 12 months or more, estimated fair value	1,384,532	1,930,105
Available-for-sale, 12 months or more, gross unrealized losses	(152,595)	(198,218)
Available-for-sale, total, estimated fair value	1,392,012	1,939,287
Available-for-sale, total, gross unrealized losses	(152,784)	(198,353)
State and political subdivisions
Available-for-sale
Available-for-sale, less than 12 months, estimated fair value	16,843	3,050
Available-for-sale, less than 12 months, gross unrealized losses	(195)	(163)
Available-for-sale, 12 months or more, estimated fair value	829,754	869,379
Available-for-sale, 12 months or more, gross unrealized losses	(157,374)	(132,378)
Available-for-sale, total, estimated fair value	846,597	872,429
Available-for-sale, total, gross unrealized losses	(157,569)	(132,541)
Other securities
Available-for-sale
Available-for-sale, less than 12 months, estimated fair value	12,912	11,016
Available-for-sale, less than 12 months, gross unrealized losses	(20)	(2,654)
Available-for-sale, 12 months or more, estimated fair value	162,803	223,025
Available-for-sale, 12 months or more, gross unrealized losses	(12,232)	(22,214)
Available-for-sale, total, estimated fair value	175,715	234,041
Available-for-sale, total, gross unrealized losses	$ (12,252)	$ (24,868)