Fair Value Measurements - Assets and Liabilities Measured at Estimated Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-Sale	$ 10,592,409	$ 10,748,961
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account	118,838	117,847
Significant Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account	18,160
U.S. Treasury and Federal Agencies [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-Sale	953,285	7,670,960
Commercial Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-Sale	525,469	574,299
Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-Sale	2,168,287	2,330,118
Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-Sale	163,546	173,584
Fair Value Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account	136,998	117,847
Debt Securities, Available-for-Sale	10,592,409	10,748,961
Equity Securities, FV-NI, Current	259,216	151,458
Real estate loans held for sale	430,720	162,393
Other assets	420,302	435,969
Total assets	11,839,645	11,616,628
Other liabilities	1,489,795	1,355,326
Total liabilities	1,489,795	1,355,326
Fair Value Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account	118,838	117,847
Equity Securities, FV-NI, Current	252,080	145,289
Total assets	370,918	263,136
Fair Value Measurements, Recurring [Member] | Significant Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading account	18,160
Debt Securities, Available-for-Sale	10,592,409	10,748,961
Equity Securities, FV-NI, Current	7,136	6,169
Real estate loans held for sale	430,720	162,393
Other assets	417,922	435,517
Total assets	11,466,347	11,353,040
Other liabilities	1,436,012	1,309,301
Total liabilities	1,436,012	1,309,301
Fair Value Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other assets	2,380	452
Total assets	2,380	452
Other liabilities	53,783	46,025
Total liabilities	53,783	46,025
Fair Value Measurements, Recurring [Member] | U.S. Treasury and Federal Agencies [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-Sale	7,735,107	7,670,960
Fair Value Measurements, Recurring [Member] | U.S. Treasury and Federal Agencies [Member] | Significant Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-Sale	7,735,107	7,670,960
Fair Value Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-Sale	525,469	574,299
Fair Value Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member] | Significant Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-Sale	525,469	574,299
Fair Value Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-Sale	2,168,287	2,330,118
Fair Value Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member] | Significant Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-Sale	2,168,287	2,330,118
Fair Value Measurements, Recurring [Member] | Other Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-Sale	163,546	173,584
Fair Value Measurements, Recurring [Member] | Other Debt Securities [Member] | Significant Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt Securities, Available-for-Sale	$ 163,546	$ 173,584