Investment Securities - Unrealized Losses and Estimated Fair Value of Investment Securities Available for Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	$ 134,631	$ 143,467
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(3,744)	(2,794)
Fair Value of Available-for-Sale Securities, 12 Months or More	2,566,329	2,887,122
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(334,860)	(333,485)
Fair Value of Available-for-Sale Securities, Total	2,700,960	3,030,589
Unrealized Losses of Available-for-Sale Securities, Total	(338,604)	(336,279)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	77,866	69,991
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(3,016)	(1,158)
Fair Value of Held-to-Maturity Securities, 12 Months or More	1,064,094	1,062,828
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(129,287)	(110,905)
Fair Value of Held-to-Maturity Securities, Total	1,141,960	1,132,819
Unrealized Losses of Held-to-Maturity Securities	(132,303)	(112,063)
U.S. government-sponsored enterprises
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	25,946	2,742
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(326)	(2)
Fair Value of Available-for-Sale Securities, 12 Months or More	161,759	180,569
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(13,746)	(17,091)
Fair Value of Available-for-Sale Securities, Total	187,705	183,311
Unrealized Losses of Available-for-Sale Securities, Total	(14,072)	(17,093)
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	40,539	40,677
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(3,021)	(2,607)
Fair Value of Held-to-Maturity Securities, Total	40,539	40,677
Unrealized Losses of Held-to-Maturity Securities	(3,021)	(2,607)
U.S. government-sponsored mortgage-backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	34,597	102,831
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(1,088)	(2,166)
Fair Value of Available-for-Sale Securities, 12 Months or More	1,215,317	1,392,318
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(202,451)	(189,391)
Fair Value of Available-for-Sale Securities, Total	1,249,914	1,495,149
Unrealized Losses of Available-for-Sale Securities, Total	(203,539)	(191,557)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	48,254	48,498
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(1,979)	(861)
Fair Value of Held-to-Maturity Securities, 12 Months or More	69,220	65,573
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(4,716)	(3,501)
Fair Value of Held-to-Maturity Securities, Total	117,474	114,071
Unrealized Losses of Held-to-Maturity Securities	(6,695)	(4,362)
Private mortgage-backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	9,491	9,298
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(129)	(226)
Fair Value of Available-for-Sale Securities, 12 Months or More	161,903	166,107
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(13,120)	(15,891)
Fair Value of Available-for-Sale Securities, Total	171,394	175,405
Unrealized Losses of Available-for-Sale Securities, Total	(13,249)	(16,117)
Non-government-sponsored asset backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	10,849	0
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(60)	0
Fair Value of Available-for-Sale Securities, 12 Months or More	92,857	213,838
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(3,374)	(7,551)
Fair Value of Available-for-Sale Securities, Total	103,706	213,838
Unrealized Losses of Available-for-Sale Securities, Total	(3,434)	(7,551)
State and political subdivisions
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	46,591	28,596
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(1,230)	(400)
Fair Value of Available-for-Sale Securities, 12 Months or More	761,289	769,860
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(84,799)	(75,531)
Fair Value of Available-for-Sale Securities, Total	807,880	798,456
Unrealized Losses of Available-for-Sale Securities, Total	(86,029)	(75,931)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	29,612	21,493
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(1,037)	(297)
Fair Value of Held-to-Maturity Securities, 12 Months or More	954,335	956,578
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(121,550)	(104,797)
Fair Value of Held-to-Maturity Securities, Total	983,947	978,071
Unrealized Losses of Held-to-Maturity Securities	(122,587)	(105,094)
Other securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	7,157	0
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(911)	0
Fair Value of Available-for-Sale Securities, 12 Months or More	173,204	164,430
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(17,370)	(28,030)
Fair Value of Available-for-Sale Securities, Total	180,361	164,430
Unrealized Losses of Available-for-Sale Securities, Total	$ (18,281)	$ (28,030)

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