Fair Value Disclosures - Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	$ 5,298,557,000	$ 5,474,359,000	$ 6,502,495,000
Loans held for sale	11,996,000	11,965,000	27,670,000
U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	488,242,000	482,549,000	301,344,000
Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	1,773,612,000	1,898,611,000	2,529,481,000
Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	2,583,170,000	2,616,566,000	3,265,191,000
Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	349,936,000	374,869,000	337,678,000
IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	827,000	400,000	276,000
Liability Derivative Fair Value	0	0	0
Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	0	85,000	2,103,000
Liability Derivative Fair Value	334,000	0	0
Fair Value, Measurements, Recurring [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	5,298,557,000	5,474,359,000	6,502,495,000
Loans held for sale	11,766,000	10,497,000	22,382,000
Liability Derivative Fair Value	(334,000)
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	488,242,000	482,549,000	301,344,000
Fair Value, Measurements, Recurring [Member] | Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	1,773,612,000	1,898,611,000	2,529,481,000
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	2,583,170,000	2,616,566,000	3,265,191,000
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	349,936,000	374,869,000	337,678,000
Fair Value, Measurements, Recurring [Member] | IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	827,000	400,000	276,000
Fair Value, Measurements, Recurring [Member] | Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value			2,103,000
Liability Derivative Fair Value		85,000
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	99,620,000	97,850,000	64,581,000
Fair Value, Measurements, Recurring [Member] | Collateralized Securities, Other [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	3,977,000	3,914,000	4,220,000
Fair Value, Measurements, Recurring [Member] | Level 1 Inputs [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	492,219,000	486,463,000	305,564,000
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	488,242,000	482,549,000	301,344,000
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:
Asset Derivative Fair Value			0
Liability Derivative Fair Value	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] | Collateralized Securities, Other [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	3,977,000	3,914,000	4,220,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	4,806,338,000	4,987,896,000	6,196,931,000
Loans held for sale	11,766,000	10,497,000	22,382,000
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	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	1,773,612,000	1,898,611,000	2,529,481,000
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	2,583,170,000	2,616,566,000	3,265,191,000
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	349,936,000	374,869,000	337,678,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	827,000	400,000	276,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value			2,103,000
Liability Derivative Fair Value	(334,000)	85,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Corporate Bonds [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	99,620,000	97,850,000	64,581,000
Fair Value, Measurements, Recurring [Member] | Level 2 Inputs [Member] | Collateralized Securities, Other [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:
Asset Derivative Fair Value			0
Liability Derivative Fair Value	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] | Collateralized Securities, Other [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	$ 0	$ 0	$ 0