Fair Value Disclosures - Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	$ 6,502,495,000	$ 6,573,179,000	$ 5,109,631,000
Loans held for sale	27,670,000	37,810,000	65,405,000
U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	301,344,000	126,841,000
Obligations of State and Political Subdivisions [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	2,529,481,000	2,753,471,000	2,517,017,000
Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	3,265,191,000	3,259,449,000	2,108,594,000
Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	337,678,000	365,120,000	447,053,000
IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	276,000	1,279,000	1,645,000
Liability Derivative Fair Value	0	0	0
Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	2,103,000	0	2,806,000
Liability Derivative Fair Value	0	147,000	0
Fair Value, Measurements, Recurring [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	6,502,495,000	6,573,179,000	5,109,631,000
Loans held for sale	22,382,000	34,122,000	61,511,000
Fair Value, Measurements, Recurring [Member] \| U.S. Treasury Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	301,344,000	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	2,529,481,000	2,753,471,000	2,517,017,000
Fair Value, Measurements, Recurring [Member] \| Residential Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	3,265,191,000	3,259,449,000	2,108,594,000
Fair Value, Measurements, Recurring [Member] \| Commercial Mortgage-Backed Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	337,678,000	365,120,000	447,053,000
Fair Value, Measurements, Recurring [Member] \| IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	276,000	1,279,000	1,645,000
Fair Value, Measurements, Recurring [Member] \| Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Liability Derivative Fair Value	2,103,000	(147,000)	2,806,000
Fair Value, Measurements, Recurring [Member] \| Corporate Bonds [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	64,581,000	63,868,000	32,490,000
Fair Value, Measurements, Recurring [Member] \| Other Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	4,220,000	4,430,000	4,477,000
Fair Value, Measurements, Recurring [Member] \| Level 1 Inputs [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	305,564,000	131,271,000	4,477,000
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	301,344,000	126,841,000
Fair Value, Measurements, Recurring [Member] \| Level 1 Inputs [Member] \| Other Securities [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	4,220,000	4,430,000	4,477,000
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	6,196,931,000	6,441,908,000	5,105,154,000
Loans held for sale	22,382,000	34,122,000	61,511,000
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	2,529,481,000	2,753,471,000	2,517,017,000
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	3,265,191,000	3,259,449,000	2,108,594,000
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	337,678,000	365,120,000	447,053,000
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| IRLCs [Member]
Available-for-sale investment securities:
Asset Derivative Fair Value	276,000	1,279,000	1,645,000
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| Forward Mortgage-Backed Securities Trades [Member]
Available-for-sale investment securities:
Liability Derivative Fair Value	2,103,000	(147,000)	2,806,000
Fair Value, Measurements, Recurring [Member] \| Level 2 Inputs [Member] \| Corporate Bonds [Member]
Available-for-sale investment securities:
Securities available-for-sale, Estimated Fair Value	$ 64,581,000	$ 63,868,000	$ 32,490,000

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Amount, after valuation allowance, of financing receivable held for sale and not part of disposal group. Excludes loan covered under loss sharing agreement and loan classified as investment in debt security.

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