Loans (Summary of Loan Portfolio) (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022
Loans [Line Items]
Total loans, net of unearned income	$ 41,023,408	$ 39,196,485	$ 37,053,103
Total loans, net of unearned income, percentage	100.00%	100.00%	100.00%
Commercial
Loans [Line Items]
Total loans, net of unearned income	$ 12,600,471	$ 12,549,164	$ 12,047,105
Total loans, net of unearned income, percentage	31.00%	32.00%	32.00%
Commercial real estate
Loans [Line Items]
Total loans, net of unearned income	$ 10,608,811	$ 9,950,947	$ 9,407,205
Total loans, net of unearned income, percentage	26.00%	25.00%	25.00%
Home equity
Loans [Line Items]
Total loans, net of unearned income	$ 336,974	$ 332,698	$ 325,826
Total loans, net of unearned income, percentage	1.00%	1.00%	1.00%
Residential real estate
Loans [Line Items]
Total loans, net of unearned income	$ 2,643,240	$ 2,372,383	$ 2,078,907
Total loans, net of unearned income, percentage	6.00%	6.00%	6.00%
Premium finance receivables | Property and casualty insurance
Loans [Line Items]
Total loans, net of unearned income	$ 6,762,698	$ 5,849,459	$ 5,541,447
Total loans, net of unearned income, percentage	16.00%	15.00%	15.00%
Premium finance receivables | Life insurance
Loans [Line Items]
Total loans, net of unearned income	$ 8,039,273	$ 8,090,998	$ 7,608,433
Total loans, net of unearned income, percentage	20.00%	21.00%	21.00%
Consumer and other
Loans [Line Items]
Total loans, net of unearned income	$ 31,941	$ 50,836	$ 44,180
Total loans, net of unearned income, percentage	0.00%	0.00%	0.00%