Securities - Securities Available for Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 13,903,318	$ 13,999,900
Gross Unrealized Gains	42,790	117,987
Gross Unrealized Losses	(457,949)	(408,746)
Fair Value	13,488,159	13,709,141
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,212,279	2,301,248
Gross Unrealized Gains	1,966	20,008
Gross Unrealized Losses	(9,328)	(441)
Fair Value	2,204,917	2,320,815
U.S. Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	48,776	62,069
Gross Unrealized Gains	66	401
Gross Unrealized Losses	(57)	(100)
Fair Value	48,785	62,370
Mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,582,743	8,427,197
Gross Unrealized Gains	22,107	71,827
Gross Unrealized Losses	(381,235)	(331,151)
Fair Value	8,223,615	8,167,873
State and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,419,723	2,494,537
Gross Unrealized Gains	18,092	24,898
Gross Unrealized Losses	(65,318)	(72,847)
Fair Value	2,372,497	2,446,588
Corporates [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	88,922	180,854
Gross Unrealized Gains	250	349
Gross Unrealized Losses	(1,863)	(4,088)
Fair Value	87,309	177,115
Collateralized loan obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	550,875	533,995
Gross Unrealized Gains	309	504
Gross Unrealized Losses	(148)	(119)
Fair Value	$ 551,036	$ 534,380

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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