Securities - Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	$ 5,217,517	$ 5,243,681	$ 5,879,040
Securities available-for-sale, Gross Unrealized Holding Gains	694	945	1,611
Securities available-for-sale, Gross Unrealized Holding Losses	(559,685)	(511,864)	(582,094)
Available-for-sale securities	4,658,526	4,732,762	5,298,557
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	445,399	496,975	508,692
Securities available-for-sale, Gross Unrealized Holding Gains	0	4	32
Securities available-for-sale, Gross Unrealized Holding Losses	(13,231)	(14,745)	(20,482)
Available-for-sale securities	432,168	482,234	488,242
Obligations of State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	1,592,523	1,621,405	1,935,401
Securities available-for-sale, Gross Unrealized Holding Gains	570	934	1,562
Securities available-for-sale, Gross Unrealized Holding Losses	(139,058)	(125,182)	(163,351)
Available-for-sale securities	1,454,035	1,497,157	1,773,612
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	2,685,896	2,716,968	2,957,314
Securities available-for-sale, Gross Unrealized Holding Gains	72	7	17
Securities available-for-sale, Gross Unrealized Holding Losses	(386,691)	(352,883)	(374,161)
Available-for-sale securities	2,299,277	2,364,092	2,583,170
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	381,198	295,663	364,956
Securities available-for-sale, Gross Unrealized Holding Gains	52	0	0
Securities available-for-sale, Gross Unrealized Holding Losses	(12,344)	(11,339)	(15,020)
Available-for-sale securities	368,906	284,324	349,936
Corporate Bonds and Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	112,501	112,670	112,677
Securities available-for-sale, Gross Unrealized Holding Gains	0	0	0
Securities available-for-sale, Gross Unrealized Holding Losses	(8,361)	(7,715)	(9,080)
Available-for-sale securities	$ 104,140	$ 104,955	$ 103,597