Securities - Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024	Jun. 30, 2024
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	$ 5,359,666	$ 5,155,305	$ 5,132,451
Securities available-for-sale, Gross Unrealized Holding Gains	11,150	673	491
Securities available-for-sale, Gross Unrealized Holding Losses	(484,268)	(538,219)	(559,918)
Estimated Fair Value	4,886,548	4,617,759	4,573,024
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	155,710	278,155	352,682
Securities available-for-sale, Gross Unrealized Holding Gains	1	2	0
Securities available-for-sale, Gross Unrealized Holding Losses	(1,876)	(4,595)	(10,706)
Estimated Fair Value	153,835	273,562	341,976
Obligations of State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	1,694,153	1,578,749	1,584,389
Securities available-for-sale, Gross Unrealized Holding Gains	743	338	420
Securities available-for-sale, Gross Unrealized Holding Losses	(173,532)	(138,842)	(139,436)
Estimated Fair Value	1,521,364	1,440,245	1,445,373
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	2,708,501	2,729,096	2,705,508
Securities available-for-sale, Gross Unrealized Holding Gains	3,521	184	71
Securities available-for-sale, Gross Unrealized Holding Losses	(300,148)	(378,746)	(389,494)
Estimated Fair Value	2,411,874	2,350,534	2,316,085
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	704,579	457,311	362,004
Securities available-for-sale, Gross Unrealized Holding Gains	6,875	99	0
Securities available-for-sale, Gross Unrealized Holding Losses	(4,436)	(9,658)	(11,982)
Estimated Fair Value	707,018	447,752	350,022
Corporate Bonds and Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	96,723	111,994	127,868
Securities available-for-sale, Gross Unrealized Holding Gains	10	50	0
Securities available-for-sale, Gross Unrealized Holding Losses	(4,276)	(6,378)	(8,300)
Estimated Fair Value	$ 92,457	$ 105,666	$ 119,568