Investment Securities - Unrealized Losses and Estimated Fair Value of Investment Securities Available for Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	$ 143,467	$ 2,255,449
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(2,794)	(143,387)
Fair Value of Available-for-Sale Securities, 12 Months or More	2,887,122	1,348,287
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(333,485)	(264,580)
Fair Value of Available-for-Sale Securities, Total	3,030,589	3,603,736
Unrealized Losses of Available-for-Sale Securities, Total	(336,279)	(407,967)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	69,991	1,102,071
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(1,158)	(161,755)
Fair Value of Held-to-Maturity Securities, 12 Months or More	1,062,828	0
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(110,905)	0
Fair Value of Held-to-Matuirty Securities, Total	1,132,819	1,102,071
Unrealized Losses of Held-to-Maturity Securities	(112,063)	(161,755)
U.S. government-sponsored enterprises
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	2,742	315,531
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(2)	(3,056)
Fair Value of Available-for-Sale Securities, 12 Months or More	180,569	128,527
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(17,091)	(20,153)
Fair Value of Available-for-Sale Securities, Total	183,311	444,058
Unrealized Losses of Available-for-Sale Securities, Total	(17,093)	(23,209)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	0	39,668
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	0	(3,349)
Fair Value of Held-to-Maturity Securities, 12 Months or More	40,677	0
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(2,607)	0
Fair Value of Held-to-Matuirty Securities, Total	40,677	39,668
Unrealized Losses of Held-to-Maturity Securities	(2,607)	(3,349)
U.S. government-sponsored mortgage-backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	102,831	850,268
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(2,166)	(46,505)
Fair Value of Available-for-Sale Securities, 12 Months or More	1,392,318	807,566
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(189,391)	(168,900)
Fair Value of Available-for-Sale Securities, Total	1,495,149	1,657,834
Unrealized Losses of Available-for-Sale Securities, Total	(191,557)	(215,405)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	48,498	106,840
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(861)	(3,756)
Fair Value of Held-to-Maturity Securities, 12 Months or More	65,573	0
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(3,501)	0
Fair Value of Held-to-Matuirty Securities, Total	114,071	106,840
Unrealized Losses of Held-to-Maturity Securities	(4,362)	(3,756)
Private mortgage-backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	9,298	179,133
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(226)	(18,302)
Fair Value of Available-for-Sale Securities, 12 Months or More	166,107	0
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(15,891)	0
Fair Value of Available-for-Sale Securities, Total	175,405	179,133
Unrealized Losses of Available-for-Sale Securities, Total	(16,117)	(18,302)
Non-government-sponsored asset backed securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	0	285,724
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	0	(9,726)
Fair Value of Available-for-Sale Securities, 12 Months or More	213,838	39,133
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(7,551)	(4,928)
Fair Value of Available-for-Sale Securities, Total	213,838	324,857
Unrealized Losses of Available-for-Sale Securities, Total	(7,551)	(14,654)
State and political subdivisions
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	28,596	485,817
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	(400)	(50,484)
Fair Value of Available-for-Sale Securities, 12 Months or More	769,860	338,638
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(75,531)	(65,214)
Fair Value of Available-for-Sale Securities, Total	798,456	824,455
Unrealized Losses of Available-for-Sale Securities, Total	(75,931)	(115,698)
Held-to-maturity:
Fair Value of Held-to-Maturity Securities, Less Than 12 Months	21,493	955,563
Unrealized Losses of Held-to-Maturity Securities, Less Than 12 Months	(297)	(154,650)
Fair Value of Held-to-Maturity Securities, 12 Months or More	956,578	0
Unrealized Losses of Held-to-Maturity Securities, 12 Months or More	(104,797)	0
Fair Value of Held-to-Matuirty Securities, Total	978,071	955,563
Unrealized Losses of Held-to-Maturity Securities	(105,094)	(154,650)
Other securities
Available-for-sale:
Fair Value of Available-for-Sale Securities, Less Than 12 Months	0	138,976
Unrealized Losses of Available-for-Sale Securities, Less Than 12 Months	0	(15,314)
Fair Value of Available-for-Sale Securities, 12 Months or More	164,430	34,423
Unrealized Losses of Available-for-Sale Securities, 12 Months or More	(28,030)	(5,385)
Fair Value of Available-for-Sale Securities, Total	164,430	173,399
Unrealized Losses of Available-for-Sale Securities, Total	$ (28,030)	$ (20,699)

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