Fair Value Disclosures - Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	$ 6,215,036,000	$ 6,573,179,000	$ 5,578,048,000
Loans held for sale	26,445,000	37,810,000	61,802,000
U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	486,358,000	126,841,000
Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	2,244,604,000	2,753,471,000	2,615,087,000
Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	2,964,904,000	3,259,449,000	2,504,186,000
Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	414,825,000	365,120,000	420,968,000
IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	1,414,000	1,279,000	2,670,000
Liability Derivative Fair Value	0	0	0
Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	58,000	0	0
Liability Derivative Fair Value	0	147,000	376,000
Fair Value, Measurements, Recurring [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	6,215,036,000	6,573,179,000	5,578,048,000
Loans held for sale	23,848,000	34,122,000	56,257,000
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	486,358,000	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	2,244,604,000	2,753,471,000	2,615,087,000
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	2,964,904,000	3,259,449,000	2,504,186,000
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	414,825,000	365,120,000	420,968,000
Fair Value, Measurements, Recurring [Member] | IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	1,414,000	1,279,000	2,670,000
Fair Value, Measurements, Recurring [Member] | Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Liability Derivative Fair Value	58,000	(147,000)	376,000
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	100,267,000	63,868,000	33,318,000
Fair Value, Measurements, Recurring [Member] | Other Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	4,078,000	4,430,000	4,489,000
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	490,436,000	131,271,000	4,489,000
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	486,358,000	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
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
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
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
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member] | Other Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	4,078,000	4,430,000	4,489,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	5,724,600,000	6,441,908,000	5,573,559,000
Loans held for sale	23,848,000	34,122,000	56,257,000
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
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	2,244,604,000	2,753,471,000	2,615,087,000
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	2,964,904,000	3,259,449,000	2,504,186,000
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	414,825,000	365,120,000	420,968,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	1,414,000	1,279,000	2,670,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Liability Derivative Fair Value	58,000	(147,000)	(376,000)
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Corporate Bonds [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	100,267,000	63,868,000	33,318,000
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
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
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
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
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
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
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