Fair Value Disclosures - Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	$ 5,745,443,000	$ 6,573,179,000	$ 6,119,984,000
Loans held for sale	18,815,000	37,810,000	47,721,000
U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	477,176,000	126,841,000
Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	2,083,812,000	2,753,471,000	2,665,367,000
Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	2,696,881,000	3,259,449,000	3,028,149,000
Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	387,346,000	365,120,000	389,016,000
IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value		1,279,000	1,701,000
Liability Derivative Fair Value	251,000	0	0
Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	1,897,000	0	828,000
Liability Derivative Fair Value		147,000	0
Fair Value, Measurements, Recurring [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	5,745,443,000	6,573,179,000	6,119,984,000
Loans held for sale	15,892,000	34,122,000	46,081,000
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	477,176,000	126,841,000
Fair Value, Measurements, Recurring [Member] | Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	2,083,812,000	2,753,471,000	2,665,367,000
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	2,696,881,000	3,259,449,000	3,028,149,000
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	387,346,000	365,120,000	389,016,000
Fair Value, Measurements, Recurring [Member] | IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	(251,000)	1,279,000	1,701,000
Fair Value, Measurements, Recurring [Member] | Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Liability Derivative Fair Value	1,897,000	(147,000)	828,000
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	96,322,000	63,868,000	32,984,000
Fair Value, Measurements, Recurring [Member] | Other Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	3,906,000	4,430,000	4,468,000
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	481,082,000	131,271,000	4,468,000
Loans held for sale	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	477,176,000	126,841,000
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Liability Derivative Fair Value	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Corporate Bonds [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Other Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	3,906,000	4,430,000	4,468,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	5,264,361,000	6,441,908,000	6,115,516,000
Loans held for sale	15,892,000	34,122,000	46,081,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	2,083,812,000	2,753,471,000	2,665,367,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	2,696,881,000	3,259,449,000	3,028,149,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	387,346,000	365,120,000	389,016,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	(251,000)	1,279,000	1,701,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Liability Derivative Fair Value	1,897,000	(147,000)	(828,000)
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Corporate Bonds [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	96,322,000	63,868,000	32,984,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Other Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	0	0	0
Loans held for sale	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Liability Derivative Fair Value	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | Corporate Bonds [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 Inputs [Member] | Other Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	$ 0	$ 0	$ 0