Fair Value Measurements - Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025	Jun. 30, 2025	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 6,467,194	$ 8,874,055	$ 7,116,087	$ 10,234,258
Securities held to maturity, net of allowance for credit losses of $500 at both June 30, 2026 and December 31, 2025	3,385,507	3,431,179
Deposits	43,334,015	42,917,864
Federal funds purchased	25,500	18,775
Repurchase agreements	4,886,598	4,525,855
Junior subordinated deferrable interest debentures	123,271	123,242
Subordinated notes	99,883	99,804
Loans, net	22,691,946	21,610,317
Carrying Amount [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	6,467,194	8,874,055
Securities held to maturity, net of allowance for credit losses of $500 at both June 30, 2026 and December 31, 2025	3,385,507	3,431,179
Accrued interest receivable	255,130	256,093
Deposits	43,334,015	42,917,864
Federal funds purchased	25,500	18,775
Repurchase agreements	4,886,598	4,525,855
Junior subordinated deferrable interest debentures	123,271	123,242
Subordinated notes	99,883	99,804
Accrued interest payable	43,694	45,737
Carrying Amount [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	22,691,946	21,610,317
Estimated Fair Value [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	6,467,194	8,874,055
Securities held to maturity, net of allowance for credit losses of $500 at both June 30, 2026 and December 31, 2025	3,250,816	3,295,431
Accrued interest receivable	255,130	256,093
Deposits	43,320,873	42,908,091
Federal funds purchased	25,500	18,775
Repurchase agreements	4,886,598	4,525,855
Junior subordinated deferrable interest debentures	123,712	123,712
Subordinated notes	99,832	100,053
Accrued interest payable	43,694	45,737
Estimated Fair Value [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	$ 22,509,277	$ 21,559,335