Fair Value Measurements (Estimated Fair Values of Financial Instruments) (Detail) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and cash equivalents	$ 8,874,055	$ 10,234,258	$ 8,687,276	$ 12,028,132
Securities held to maturity	3,431,179	3,533,775
Deposits	42,917,864	42,722,748
Federal funds purchased	18,775	21,975
Repurchase agreements	4,525,855	4,342,941
Junior subordinated deferrable interest debentures	123,242	123,184
Subordinated notes	99,804	99,648
Net loans	21,610,317	20,484,662
Carrying Amount [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and cash equivalents	8,874,055	10,234,258
Securities held to maturity	3,431,179	3,533,775
Accrued interest receivable	256,093	236,591
Deposits	42,917,864	42,722,748
Federal funds purchased	18,775	21,975
Repurchase agreements	4,525,855	4,342,941
Junior subordinated deferrable interest debentures	123,242	123,184
Subordinated notes	99,804	99,648
Accrued interest payable	45,737	58,870
Carrying Amount [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	21,610,317	20,484,662
Estimated Fair Value [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and cash equivalents	8,874,055	10,234,258
Securities held to maturity	3,295,431	3,360,546
Accrued interest receivable	256,093	236,591
Deposits	42,908,091	42,712,907
Federal funds purchased	18,775	21,975
Repurchase agreements	4,525,855	4,342,941
Junior subordinated deferrable interest debentures	123,712	123,712
Subordinated notes	100,053	98,453
Accrued interest payable	45,737	58,870
Estimated Fair Value [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	$ 21,559,335	$ 20,066,512