Securities - Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	$ 5,879,040	$ 6,152,348	$ 6,767,967
Securities available-for-sale, Gross Unrealized Holding Gains	1,611	1,237	29,691
Securities available-for-sale, Gross Unrealized Holding Losses	(582,094)	(679,226)	(295,163)
Securities available-for-sale, Estimated Fair Value	5,298,557	5,474,359	6,502,495
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	508,692	508,275	311,860
Securities available-for-sale, Gross Unrealized Holding Gains	32	11	0
Securities available-for-sale, Gross Unrealized Holding Losses	(20,482)	(25,737)	(10,516)
Securities available-for-sale, Estimated Fair Value	488,242	482,549	301,344
Obligations of State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	1,935,401	2,104,193	2,590,308
Securities available-for-sale, Gross Unrealized Holding Gains	1,562	1,217	26,628
Securities available-for-sale, Gross Unrealized Holding Losses	(163,351)	(206,799)	(87,455)
Securities available-for-sale, Estimated Fair Value	1,773,612	1,898,611	2,529,481
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	2,957,314	3,034,120	3,450,006
Securities available-for-sale, Gross Unrealized Holding Gains	17	8	2,139
Securities available-for-sale, Gross Unrealized Holding Losses	(374,161)	(417,562)	(186,954)
Securities available-for-sale, Estimated Fair Value	2,583,170	2,616,566	3,265,191
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	364,956	392,914	341,506
Securities available-for-sale, Gross Unrealized Holding Gains	0	1	924
Securities available-for-sale, Gross Unrealized Holding Losses	(15,020)	(18,046)	(4,752)
Securities available-for-sale, Estimated Fair Value	349,936	374,869	337,678
Corporate Bonds and Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	112,677	112,846	74,287
Securities available-for-sale, Gross Unrealized Holding Gains	0	0	0
Securities available-for-sale, Gross Unrealized Holding Losses	(9,080)	(11,082)	(5,486)
Securities available-for-sale, Estimated Fair Value	$ 103,597	$ 101,764	$ 68,801