Investment Securities - Securities With Unrealized Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	$ 27,841	$ 37,952
Available-for-sale, less than 12 months, gross unrealized losses	(303)	(411)
Available-for-sale, 12 months or more, estimated fair value	2,384,386	2,429,271
Available-for-sale, 12 months or more, gross unrealized losses	(337,094)	(323,244)
Available-for-sale, total, estimated fair value	2,412,227	2,467,223
Available-for-sale, total, gross unrealized losses	(337,397)	(323,655)
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
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	699	996
Available-for-sale, 12 months or more, gross unrealized losses	(1)	(3)
Available-for-sale, total, estimated fair value	699	996
Available-for-sale, total, gross unrealized losses	(1)	(3)
U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	1,708	717
Available-for-sale, less than 12 months, gross unrealized losses	(21)	(7)
Available-for-sale, 12 months or more, estimated fair value	49,184	51,186
Available-for-sale, 12 months or more, gross unrealized losses	(837)	(1,040)
Available-for-sale, total, estimated fair value	50,892	51,903
Available-for-sale, total, gross unrealized losses	(858)	(1,047)
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	7,055	7,480
Available-for-sale, less than 12 months, gross unrealized losses	(15)	(189)
Available-for-sale, 12 months or more, estimated fair value	1,364,722	1,384,532
Available-for-sale, 12 months or more, gross unrealized losses	(127,755)	(152,595)
Available-for-sale, total, estimated fair value	1,371,777	1,392,012
Available-for-sale, total, gross unrealized losses	(127,770)	(152,784)
State and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	14,153	16,843
Available-for-sale, less than 12 months, gross unrealized losses	(192)	(195)
Available-for-sale, 12 months or more, estimated fair value	806,319	829,754
Available-for-sale, 12 months or more, gross unrealized losses	(198,387)	(157,374)
Available-for-sale, total, estimated fair value	820,472	846,597
Available-for-sale, total, gross unrealized losses	(198,579)	(157,569)
Other securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	4,925	12,912
Available-for-sale, less than 12 months, gross unrealized losses	(75)	(20)
Available-for-sale, 12 months or more, estimated fair value	163,462	162,803
Available-for-sale, 12 months or more, gross unrealized losses	(10,114)	(12,232)
Available-for-sale, total, estimated fair value	168,387	175,715
Available-for-sale, total, gross unrealized losses	$ (10,189)	$ (12,252)