Goodwill and Other Intangible Assets (Gross Carrying Value And Accumulated Amortization Of Other Intangible Assets) (Detail) - USD ($) $ in Thousands	Jan. 24, 2024	Mar. 31, 2024	Dec. 31, 2023
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount		$ 489,937	$ 301,037
Accumulated Amortization		107,096	97,902
Net Carrying Amount		382,841	203,135
Core deposits (1)
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount		328,837	146,037
Accumulated Amortization		59,239	53,986
Net Carrying Amount		269,598	92,051
Core deposits (1) | Ametros
Finite-Lived Intangible Assets [Line Items]
Acquired intangible assets, useful life	25 years
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	$ 182,800
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount		151,000	151,000
Accumulated Amortization		46,654	43,116
Net Carrying Amount		104,346	107,884
Noncompete Agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount		4,000	4,000
Accumulated Amortization		1,000	800
Net Carrying Amount		3,000	3,200
Trade Names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount		6,100	0
Accumulated Amortization		203	0
Net Carrying Amount		$ 5,897	$ 0
Trade Names | Ametros
Finite-Lived Intangible Assets [Line Items]
Acquired intangible assets, useful life	5 years
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	$ 6,100