Investment Securities - Unrealized Losses and Estimated Fair Value of Investment Securities Available for Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	$ 209,223	$ 134,631
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(2,248)	(3,744)
Fair Value of Available-for-Sale Securities, 12 Months or More	2,533,587	2,566,329
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(295,245)	(334,860)
Fair Value of Available-for-Sale Securities, Total	2,742,810	2,700,960
Unrealized Losses of Available-for-Sale Securities, Total	(297,493)	(338,604)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	69,880	77,866
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(1,633)	(3,016)
Fair Value of Held-to-Maturity Securities, 12 Months or More	1,076,183	1,064,094
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(115,093)	(129,287)
Fair Value of Held-to-Maturity Securities, Total	1,146,063	1,141,960
Unrealized Losses of Held-to-Maturity Securities	(116,726)	(132,303)
U.S. government-sponsored enterprises
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	24,208	25,946
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(215)	(326)
Fair Value of Available-for-Sale Securities, 12 Months or More	163,377	161,759
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(11,305)	(13,746)
Fair Value of Available-for-Sale Securities, Total	187,585	187,705
Unrealized Losses of Available-for-Sale Securities, Total	(11,520)	(14,072)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	0	0
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	0	0
Fair Value of Held-to-Maturity Securities, 12 Months or More	41,380	40,539
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(2,249)	(3,021)
Fair Value of Held-to-Maturity Securities, Total	41,380	40,539
Unrealized Losses of Held-to-Maturity Securities	(2,249)	(3,021)
U.S. government-sponsored mortgage-backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	33,859	34,597
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(214)	(1,088)
Fair Value of Available-for-Sale Securities, 12 Months or More	1,186,597	1,215,317
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(169,312)	(202,451)
Fair Value of Available-for-Sale Securities, Total	1,220,456	1,249,914
Unrealized Losses of Available-for-Sale Securities, Total	(169,526)	(203,539)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	50,635	48,254
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(866)	(1,979)
Fair Value of Held-to-Maturity Securities, 12 Months or More	62,274	69,220
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(3,643)	(4,716)
Fair Value of Held-to-Maturity Securities, Total	112,909	117,474
Unrealized Losses of Held-to-Maturity Securities	(4,509)	(6,695)
Private mortgage-backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	0	9,491
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	0	(129)
Fair Value of Available-for-Sale Securities, 12 Months or More	161,674	161,903
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(10,541)	(13,120)
Fair Value of Available-for-Sale Securities, Total	161,674	171,394
Unrealized Losses of Available-for-Sale Securities, Total	(10,541)	(13,249)
Non-government-sponsored asset backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	105,201	10,849
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(223)	(60)
Fair Value of Available-for-Sale Securities, 12 Months or More	85,633	92,857
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(2,549)	(3,374)
Fair Value of Available-for-Sale Securities, Total	190,834	103,706
Unrealized Losses of Available-for-Sale Securities, Total	(2,772)	(3,434)
State and political subdivisions
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	40,072	46,591
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(1,332)	(1,230)
Fair Value of Available-for-Sale Securities, 12 Months or More	757,250	761,289
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(86,529)	(84,799)
Fair Value of Available-for-Sale Securities, Total	797,322	807,880
Unrealized Losses of Available-for-Sale Securities, Total	(87,861)	(86,029)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	19,245	29,612
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(767)	(1,037)
Fair Value of Held-to-Maturity Securities, 12 Months or More	972,529	954,335
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(109,201)	(121,550)
Fair Value of Held-to-Maturity Securities, Total	991,774	983,947
Unrealized Losses of Held-to-Maturity Securities	(109,968)	(122,587)
Other securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	5,883	7,157
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(264)	(911)
Fair Value of Available-for-Sale Securities, 12 Months or More	179,056	173,204
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(15,009)	(17,370)
Fair Value of Available-for-Sale Securities, Total	184,939	180,361
Unrealized Losses of Available-for-Sale Securities, Total	$ (15,273)	$ (18,281)

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