Securities - Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	$ 5,132,451	$ 5,243,681	$ 5,687,352
Securities available-for-sale, Gross Unrealized Holding Gains	491	945	407
Securities available-for-sale, Gross Unrealized Holding Losses	(559,918)	(511,864)	(621,497)
Estimated Fair Value	4,573,024	4,732,762	5,066,262
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	352,682	496,975	508,124
Securities available-for-sale, Gross Unrealized Holding Gains	0	4	0
Securities available-for-sale, Gross Unrealized Holding Losses	(10,706)	(14,745)	(24,348)
Estimated Fair Value	341,976	482,234	483,776
Obligations of State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	1,584,389	1,621,405	1,859,193
Securities available-for-sale, Gross Unrealized Holding Gains	420	934	405
Securities available-for-sale, Gross Unrealized Holding Losses	(139,436)	(125,182)	(166,634)
Estimated Fair Value	1,445,373	1,497,157	1,692,964
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	2,705,508	2,716,968	2,875,699
Securities available-for-sale, Gross Unrealized Holding Gains	71	7	2
Securities available-for-sale, Gross Unrealized Holding Losses	(389,494)	(352,883)	(402,760)
Estimated Fair Value	2,316,085	2,364,092	2,472,941
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	362,004	295,663	331,829
Securities available-for-sale, Gross Unrealized Holding Gains	0	0	0
Securities available-for-sale, Gross Unrealized Holding Losses	(11,982)	(11,339)	(17,442)
Estimated Fair Value	350,022	284,324	314,387
Corporate Bonds and Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	127,868	112,670	112,507
Securities available-for-sale, Gross Unrealized Holding Gains	0	0	0
Securities available-for-sale, Gross Unrealized Holding Losses	(8,300)	(7,715)	(10,313)
Estimated Fair Value	$ 119,568	$ 104,955	$ 102,194