Fair Value Measurements - Assets and Liabilities Measured at Estimated Fair Value on Recurring Basis (Detail) - Recurring - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Fair Value Measurements
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account	$ 102,000	$ 106,000
Investment securities available for sale:	16,727,000	10,440,000
Equity securities	257,000	268,000
Real estate loans held for sale	958,000	379,000
Other assets	286,000	324,000
Total assets	18,330,000	11,517,000
Other liabilities	679,000	943,000
Total liabilities	679,000	943,000
Fair Value Measurements | U.S. Treasury and federal agencies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	7,860,000	7,705,000
Fair Value Measurements | Commercial
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	3,177,000	416,000
Fair Value Measurements | Residential
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	5,589,000	2,154,000
Fair Value Measurements | Other debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	101,000	165,000
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account	102,000	101,000
Investment securities available for sale:	0	0
Equity securities	244,000	258,000
Real estate loans held for sale	0	0
Other assets	0	0
Total assets	346,000	359,000
Other liabilities	0	0
Total liabilities	0	0
Level 1 | U.S. Treasury and federal agencies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	0	0
Level 1 | Commercial
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	0	0
Level 1 | Residential
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	0	0
Level 1 | Other debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	0	0
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account	0	5,000
Investment securities available for sale:	16,727,000	10,440,000
Equity securities	13,000	10,000
Real estate loans held for sale	958,000	379,000
Other assets	257,000	309,000
Total assets	17,955,000	11,143,000
Other liabilities	658,000	911,000
Total liabilities	658,000	911,000
Level 2 | U.S. Treasury and federal agencies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	7,860,000	7,705,000
Level 2 | Commercial
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	3,177,000	416,000
Level 2 | Residential
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	5,589,000	2,154,000
Level 2 | Other debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	101,000	165,000
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account	0	0
Investment securities available for sale:	0	0
Equity securities	0	0
Real estate loans held for sale	0	0
Other assets	29,000	15,000
Total assets	29,000	15,000
Other liabilities	21,000	32,000
Total liabilities	21,000	32,000
Level 3 | U.S. Treasury and federal agencies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	0	0
Level 3 | Commercial
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	0	0
Level 3 | Residential
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	0	0
Level 3 | Other debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	$ 0	$ 0