Investment Securities - Unrealized Losses and Estimated Fair Value of Investment Securities Available for Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	$ 144,981	$ 134,631
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(2,947)	(3,744)
Fair Value of Available-for-Sale Securities, 12 Months or More	2,421,104	2,566,329
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(309,389)	(334,860)
Fair Value of Available-for-Sale Securities, Total	2,566,085	2,700,960
Unrealized Losses of Available-for-Sale Securities, Total	(312,336)	(338,604)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	72,621	77,866
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(2,395)	(3,016)
Fair Value of Held-to-Maturity Securities, 12 Months or More	1,045,183	1,064,094
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(135,926)	(129,287)
Fair Value of Held-to-Maturity Securities, Total	1,117,804	1,141,960
Unrealized Losses of Held-to-Maturity Securities	(138,321)	(132,303)
U.S. government-sponsored enterprises
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	13,552	25,946
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(134)	(326)
Fair Value of Available-for-Sale Securities, 12 Months or More	163,744	161,759
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(10,180)	(13,746)
Fair Value of Available-for-Sale Securities, Total	177,296	187,705
Unrealized Losses of Available-for-Sale Securities, Total	(10,314)	(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	41,608	40,539
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(2,091)	(3,021)
Fair Value of Held-to-Maturity Securities, Total	41,608	40,539
Unrealized Losses of Held-to-Maturity Securities	(2,091)	(3,021)
U.S. government-sponsored mortgage-backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	47,193	34,597
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(371)	(1,088)
Fair Value of Available-for-Sale Securities, 12 Months or More	1,131,637	1,215,317
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(171,095)	(202,451)
Fair Value of Available-for-Sale Securities, Total	1,178,830	1,249,914
Unrealized Losses of Available-for-Sale Securities, Total	(171,466)	(203,539)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	47,304	48,254
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(1,172)	(1,979)
Fair Value of Held-to-Maturity Securities, 12 Months or More	60,994	69,220
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(4,131)	(4,716)
Fair Value of Held-to-Maturity Securities, Total	108,298	117,474
Unrealized Losses of Held-to-Maturity Securities	(5,303)	(6,695)
Private mortgage-backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	9,656	9,491
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(11)	(129)
Fair Value of Available-for-Sale Securities, 12 Months or More	145,926	161,903
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(10,678)	(13,120)
Fair Value of Available-for-Sale Securities, Total	155,582	171,394
Unrealized Losses of Available-for-Sale Securities, Total	(10,689)	(13,249)
Non-government-sponsored asset backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	13,916	10,849
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(9)	(60)
Fair Value of Available-for-Sale Securities, 12 Months or More	69,888	92,857
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(1,729)	(3,374)
Fair Value of Available-for-Sale Securities, Total	83,804	103,706
Unrealized Losses of Available-for-Sale Securities, Total	(1,738)	(3,434)
State and political subdivisions
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	57,154	46,591
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(2,364)	(1,230)
Fair Value of Available-for-Sale Securities, 12 Months or More	728,273	761,289
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(100,707)	(84,799)
Fair Value of Available-for-Sale Securities, Total	785,427	807,880
Unrealized Losses of Available-for-Sale Securities, Total	(103,071)	(86,029)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	25,317	29,612
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(1,223)	(1,037)
Fair Value of Held-to-Maturity Securities, 12 Months or More	942,581	954,335
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(129,704)	(121,550)
Fair Value of Held-to-Maturity Securities, Total	967,898	983,947
Unrealized Losses of Held-to-Maturity Securities	(130,927)	(122,587)
Other securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	3,510	7,157
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(58)	(911)
Fair Value of Available-for-Sale Securities, 12 Months or More	181,636	173,204
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(15,000)	(17,370)
Fair Value of Available-for-Sale Securities, Total	185,146	180,361
Unrealized Losses of Available-for-Sale Securities, Total	$ (15,058)	$ (18,281)

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