Fair Value Measurements - Assets and Liabilities Measured at Estimated Fair Value on Recurring Basis (Detail) - Recurring - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Fair Value Measurements
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account	$ 99,000	$ 106,000
Investment securities available for sale:	13,892,000	10,440,000
Equity securities	280,000	268,000
Real estate loans held for sale	377,000	379,000
Other assets	295,000	324,000
Total assets	14,943,000	11,517,000
Other liabilities	1,041,000	943,000
Total liabilities	1,041,000	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:	7,736,000	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:	2,089,000	416,000
Fair Value Measurements | Residential
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	3,966,000	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	99,000	101,000
Investment securities available for sale:	0	0
Equity securities	265,000	258,000
Real estate loans held for sale	0	0
Other assets	0	0
Total assets	364,000	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:	13,892,000	10,440,000
Equity securities	15,000	10,000
Real estate loans held for sale	377,000	379,000
Other assets	280,000	309,000
Total assets	14,564,000	11,143,000
Other liabilities	1,012,000	911,000
Total liabilities	1,012,000	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:	7,736,000	7,705,000
Level 2 | Commercial
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	2,089,000	416,000
Level 2 | Residential
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment securities available for sale:	3,966,000	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	15,000	15,000
Total assets	15,000	15,000
Other liabilities	29,000	32,000
Total liabilities	29,000	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