Securities - Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	$ 5,687,352	$ 6,152,348	$ 6,722,336
Securities available-for-sale, Gross Unrealized Holding Gains	407	1,237	8,712
Securities available-for-sale, Gross Unrealized Holding Losses	(621,497)	(679,226)	(516,012)
Securities available-for-sale, Estimated Fair Value	5,066,262	5,474,359	6,215,036
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	508,124	508,275	501,098
Securities available-for-sale, Gross Unrealized Holding Gains	0	11	12
Securities available-for-sale, Gross Unrealized Holding Losses	(24,348)	(25,737)	(14,752)
Securities available-for-sale, Estimated Fair Value	483,776	482,549	486,358
Obligations of State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	1,859,193	2,104,193	2,419,232
Securities available-for-sale, Gross Unrealized Holding Gains	405	1,217	7,737
Securities available-for-sale, Gross Unrealized Holding Losses	(166,634)	(206,799)	(182,365)
Securities available-for-sale, Estimated Fair Value	1,692,964	1,898,611	2,244,604
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	2,875,699	3,034,120	3,265,654
Securities available-for-sale, Gross Unrealized Holding Gains	2	8	399
Securities available-for-sale, Gross Unrealized Holding Losses	(402,760)	(417,562)	(301,149)
Securities available-for-sale, Estimated Fair Value	2,472,941	2,616,566	2,964,904
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	331,829	392,914	423,168
Securities available-for-sale, Gross Unrealized Holding Gains	0	1	476
Securities available-for-sale, Gross Unrealized Holding Losses	(17,442)	(18,046)	(8,819)
Securities available-for-sale, Estimated Fair Value	314,387	374,869	414,825
Corporate Bonds and Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	112,507	112,846	113,184
Securities available-for-sale, Gross Unrealized Holding Gains	0	0	88
Securities available-for-sale, Gross Unrealized Holding Losses	(10,313)	(11,082)	(8,927)
Securities available-for-sale, Estimated Fair Value	$ 102,194	$ 101,764	$ 104,345