Fair Value Measurements - Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 7,144,411	$ 8,874,055	$ 7,853,408	$ 10,234,258
Securities held to maturity, net of allowance for credit losses of $500 at both March 31, 2026 and December 31, 2025	3,405,500	3,431,179
Deposits	42,836,174	42,917,864
Federal funds purchased	25,350	18,775
Repurchase agreements	4,101,707	4,525,855
Junior subordinated deferrable interest debentures	123,256	123,242
Subordinated notes	99,843	99,804
Loans, net	22,146,204	21,610,317
Carrying Amount [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	7,144,411	8,874,055
Securities held to maturity, net of allowance for credit losses of $500 at both March 31, 2026 and December 31, 2025	3,405,500	3,431,179
Accrued interest receivable	191,988	256,093
Deposits	42,836,174	42,917,864
Federal funds purchased	25,350	18,775
Repurchase agreements	4,101,707	4,525,855
Junior subordinated deferrable interest debentures	123,256	123,242
Subordinated notes	99,843	99,804
Accrued interest payable	40,395	45,737
Carrying Amount [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	22,146,204	21,610,317
Estimated Fair Value [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	7,144,411	8,874,055
Securities held to maturity, net of allowance for credit losses of $500 at both March 31, 2026 and December 31, 2025	3,217,467	3,295,431
Accrued interest receivable	191,988	256,093
Deposits	42,824,987	42,908,091
Federal funds purchased	25,350	18,775
Repurchase agreements	4,101,707	4,525,855
Junior subordinated deferrable interest debentures	123,712	123,712
Subordinated notes	100,285	100,053
Accrued interest payable	40,395	45,737
Estimated Fair Value [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	$ 21,978,515	$ 21,559,335