Fair Value Disclosures - Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	$ 4,732,762,000	$ 5,474,359,000
Loans held-for-sale	(14,253,000)	(11,965,000)
Obligations of State and Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	1,497,157,000	1,898,611,000
Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	2,364,092,000	2,616,566,000
Commercial Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	284,324,000	374,869,000
IRLCs [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Asset Derivative Fair Value	427,000	400,000
Liability Derivative Fair Value	0	0
Forward Mortgage-Backed Securities Trades [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Asset Derivative Fair Value	0	85,000
Liability Derivative Fair Value	288,000	0
U.S. Treasury securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	482,234,000	482,549,000
Level 1 Inputs [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	0
Level 3 Inputs [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	0
Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	4,732,762,000	5,474,359,000
Loans held-for-sale	(11,077,000)	(10,497,000)
Fair Value, Measurements, Recurring [Member] | Obligations of State and Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	1,497,157,000	1,898,611,000
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	2,364,092,000	2,616,566,000
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	284,324,000	374,869,000
Fair Value, Measurements, Recurring [Member] | IRLCs [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Asset Derivative Fair Value	427,000	400,000
Fair Value, Measurements, Recurring [Member] | Forward Mortgage-Backed Securities Trades [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liability Derivative Fair Value	(288,000)	85,000
Fair Value, Measurements, Recurring [Member] | U.S. Treasury securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	482,234,000	482,549,000
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	100,471,000	97,850,000
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	486,718,000	486,463,000
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | U.S. Treasury securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	482,234,000	482,549,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	4,246,044,000	4,987,896,000
Loans held-for-sale	(11,077,000)	(10,497,000)
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Obligations of State and Political Subdivisions [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	1,497,157,000	1,898,611,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	2,364,092,000	2,616,566,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	284,324,000	374,869,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | IRLCs [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Asset Derivative Fair Value	427,000	400,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liability Derivative Fair Value	(288,000)	85,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Corporate Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	100,471,000	97,850,000
Other Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	4,484,000	3,914,000
Other Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value	$ 4,484,000	3,914,000
Other Securities [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale, at fair value		$ 0