Loans - Weighted Average Risk Grades for All Commercial Loans by Class (Detail) $ in Thousands	Sep. 30, 2026 USD ($) Grade	Dec. 31, 2025 USD ($) Grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	$ 23,656,967	$ 21,891,812
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6.45	6.44
Loans, net of unearned discounts	$ 6,467,069	$ 6,306,980
Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6.08	6.16
Loans, net of unearned discounts	$ 1,150,093	$ 1,094,669
Commercial Real Estate Owner Occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	7.09	7.08
Loans, net of unearned discounts	$ 4,402,147	$ 3,987,913
Commercial Real Estate Non-Owner Occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	7.16	7.18
Loans, net of unearned discounts	$ 4,218,556	$ 3,773,028
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	7.83	7.78
Loans, net of unearned discounts	$ 2,757,013	$ 2,549,869
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	7.29	7.29
Loans, net of unearned discounts	$ 11,377,716	$ 10,310,810
Risk Grade One To Eight [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6.18	6.06
Loans, net of unearned discounts	$ 5,998,560	$ 5,663,146
Risk Grade One To Eight [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	5.85	5.86
Loans, net of unearned discounts	$ 1,081,695	$ 1,010,179
Risk Grade One To Eight [Member] | Commercial Real Estate Owner Occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6.84	6.77
Loans, net of unearned discounts	$ 4,050,054	$ 3,608,005
Risk Grade One To Eight [Member] | Commercial Real Estate Non-Owner Occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	7.01	6.96
Loans, net of unearned discounts	$ 4,035,341	$ 3,494,323
Risk Grade One To Eight [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	7.53	7.61
Loans, net of unearned discounts	$ 2,393,993	$ 2,319,413
Risk Grade One To Eight [Member] | Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade		7.05
Loans, net of unearned discounts		$ 9,421,741
Risk Grade Nine [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	9.00	9.00
Loans, net of unearned discounts	$ 185,433	$ 384,532
Risk Grade Nine [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	9.00	9.00
Loans, net of unearned discounts	$ 23,870	$ 35,392
Risk Grade Nine [Member] | Commercial Real Estate Owner Occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	9.00	9.00
Loans, net of unearned discounts	$ 141,340	$ 163,132
Risk Grade Nine [Member] | Commercial Real Estate Non-Owner Occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	9.00	9.00
Loans, net of unearned discounts	$ 57,035	$ 75,560
Risk Grade Nine [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	9.00	9.00
Loans, net of unearned discounts	$ 151,097	$ 127,496
Risk Grade Nine [Member] | Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade		9.00
Loans, net of unearned discounts		$ 366,188
Risk Grade Ten [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	10.00	10.00
Loans, net of unearned discounts	$ 175,843	$ 94,182
Risk Grade Ten [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	10.00	10.00
Loans, net of unearned discounts	$ 38,660	$ 40,813
Risk Grade Ten [Member] | Commercial Real Estate Owner Occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	10.00	10.00
Loans, net of unearned discounts	$ 83,999	$ 64,117
Risk Grade Ten [Member] | Commercial Real Estate Non-Owner Occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	10.00	10.00
Loans, net of unearned discounts	$ 4,530	$ 143,606
Risk Grade Ten [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	10.00	10.00
Loans, net of unearned discounts	$ 151,035	$ 88,400
Risk Grade Ten [Member] | Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade		10.00
Loans, net of unearned discounts		$ 296,123
Risk Grade Eleven [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	11.00	11.00
Loans, net of unearned discounts	$ 86,545	$ 114,461
Risk Grade Eleven [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	11.00	11.00
Loans, net of unearned discounts	$ 3,650	$ 5,262
Risk Grade Eleven [Member] | Commercial Real Estate Owner Occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	11.00	11.00
Loans, net of unearned discounts	$ 114,916	$ 145,078
Risk Grade Eleven [Member] | Commercial Real Estate Non-Owner Occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	11.00	11.00
Loans, net of unearned discounts	$ 117,197	$ 59,074
Risk Grade Eleven [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	11.00	11.00
Loans, net of unearned discounts	$ 41,532	$ 12,686
Risk Grade Eleven [Member] | Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade		11.00
Loans, net of unearned discounts		$ 216,838
Risk Grade Twelve [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	12.00	12.00
Loans, net of unearned discounts	$ 15,009	$ 34,041
Risk Grade Twelve [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	12.00	12.00
Loans, net of unearned discounts	$ 2,218	$ 2,323
Risk Grade Twelve [Member] | Commercial Real Estate Owner Occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	12.00	12.00
Loans, net of unearned discounts	$ 11,216	$ 6,859
Risk Grade Twelve [Member] | Commercial Real Estate Non-Owner Occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	12.00	12.00
Loans, net of unearned discounts	$ 4,453	$ 465
Risk Grade Twelve [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	12.00	12.00
Loans, net of unearned discounts	$ 17,943	$ 1,361
Risk Grade Twelve [Member] | Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade		12.00
Loans, net of unearned discounts		$ 8,685
Risk Grade Thirteen [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	13.00	13.00
Loans, net of unearned discounts	$ 5,679	$ 16,618
Risk Grade Thirteen [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	13.00	13.00
Loans, net of unearned discounts	$ 0	$ 700
Risk Grade Thirteen [Member] | Commercial Real Estate Owner Occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	13.00	13.00
Loans, net of unearned discounts	$ 622	$ 722
Risk Grade Thirteen [Member] | Commercial Real Estate Non-Owner Occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	13.00	13.00
Loans, net of unearned discounts	$ 0	$ 0
Risk Grade Thirteen [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	13.00	13.00
Loans, net of unearned discounts	$ 1,413	$ 513
Risk Grade Thirteen [Member] | Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade		13.00
Loans, net of unearned discounts		$ 1,235