Securities - Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	$ 5,253,099	$ 5,155,305	$ 5,217,517
Securities available-for-sale, Gross Unrealized Holding Gains	6,472	673	694
Securities available-for-sale, Gross Unrealized Holding Losses	(499,140)	(538,219)	(559,685)
Estimated Fair Value	4,760,431	4,617,759	4,658,526
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	216,650	278,155	445,399
Securities available-for-sale, Gross Unrealized Holding Gains	3	2	0
Securities available-for-sale, Gross Unrealized Holding Losses	(2,979)	(4,595)	(13,231)
Estimated Fair Value	213,674	273,562	432,168
Obligations of State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	1,569,885	1,578,749	1,592,523
Securities available-for-sale, Gross Unrealized Holding Gains	239	338	570
Securities available-for-sale, Gross Unrealized Holding Losses	(160,637)	(138,842)	(139,058)
Estimated Fair Value	1,409,487	1,440,245	1,454,035
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	2,727,421	2,729,096	2,685,896
Securities available-for-sale, Gross Unrealized Holding Gains	2,126	184	72
Securities available-for-sale, Gross Unrealized Holding Losses	(324,666)	(378,746)	(386,691)
Estimated Fair Value	2,404,881	2,350,534	2,299,277
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	627,318	457,311	381,198
Securities available-for-sale, Gross Unrealized Holding Gains	4,040	99	52
Securities available-for-sale, Gross Unrealized Holding Losses	(5,697)	(9,658)	(12,344)
Estimated Fair Value	625,661	447,752	368,906
Corporate Bonds and Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	111,825	111,994	112,501
Securities available-for-sale, Gross Unrealized Holding Gains	64	50	0
Securities available-for-sale, Gross Unrealized Holding Losses	(5,161)	(6,378)	(8,361)
Estimated Fair Value	$ 106,728	$ 105,666	$ 104,140