Loans - Age Analysis of Past Due Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2026	Dec. 31, 2025
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	$ 23,656,967	$ 21,891,812
Financing Receivable, Excluding Accrued Interest, 90 Days or More Past Due, Still Accruing	83,792
Commercial Portfolio Segment [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	6,467,069	6,306,980
Financing Receivable, Excluding Accrued Interest, 90 Days or More Past Due, Still Accruing	11,051
Commercial and Industrial Total Energy Loans [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	1,150,093	1,094,669
Financing Receivable, Excluding Accrued Interest, 90 Days or More Past Due, Still Accruing	0
Commercial Real Estate Owner Occupied
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	4,402,147	3,987,913
Financing Receivable, Excluding Accrued Interest, 90 Days or More Past Due, Still Accruing	7,771
Commercial Real Estate Non-Owner Occupied
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	4,218,556	3,773,028
Financing Receivable, Excluding Accrued Interest, 90 Days or More Past Due, Still Accruing	55,347
Construction Loans [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	2,757,013	2,549,869
Financing Receivable, Excluding Accrued Interest, 90 Days or More Past Due, Still Accruing	1,834
Total consumer real estate loans [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	4,193,379	3,718,668
Financing Receivable, Excluding Accrued Interest, 90 Days or More Past Due, Still Accruing	7,271
Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	468,710	$ 460,685
Financing Receivable, Excluding Accrued Interest, 90 Days or More Past Due, Still Accruing	518
Financing Receivables, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	106,181
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	39,663
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial and Industrial Total Energy Loans [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	5,076
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial Real Estate Owner Occupied
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	11,514
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial Real Estate Non-Owner Occupied
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	9,766
Financing Receivables, 30 to 89 Days Past Due [Member] | Construction Loans [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	5,065
Financing Receivables, 30 to 89 Days Past Due [Member] | Total consumer real estate loans [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	26,679
Financing Receivables, 30 to 89 Days Past Due [Member] | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	8,418
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	134,646
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	25,569
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial and Industrial Total Energy Loans [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	2,218
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Real Estate Owner Occupied
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	17,012
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Real Estate Non-Owner Occupied
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	59,439
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Construction Loans [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	17,874
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Total consumer real estate loans [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	11,845
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	689
Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	240,827
Financial Asset, Past Due | Commercial Portfolio Segment [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	65,232
Financial Asset, Past Due | Commercial and Industrial Total Energy Loans [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	7,294
Financial Asset, Past Due | Commercial Real Estate Owner Occupied
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	28,526
Financial Asset, Past Due | Commercial Real Estate Non-Owner Occupied
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	69,205
Financial Asset, Past Due | Construction Loans [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	22,939
Financial Asset, Past Due | Total consumer real estate loans [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	38,524
Financial Asset, Past Due | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	9,107
Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	23,416,140
Financial Asset, Not Past Due | Commercial Portfolio Segment [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	6,401,837
Financial Asset, Not Past Due | Commercial and Industrial Total Energy Loans [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	1,142,799
Financial Asset, Not Past Due | Commercial Real Estate Owner Occupied
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	4,373,621
Financial Asset, Not Past Due | Commercial Real Estate Non-Owner Occupied
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	4,149,351
Financial Asset, Not Past Due | Construction Loans [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	2,734,074
Financial Asset, Not Past Due | Total consumer real estate loans [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	4,154,855
Financial Asset, Not Past Due | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Loans, net of unearned discounts	$ 459,603