Loans (Summary of Loan Portfolio) (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Loans [Line Items]
Total loans, net of unearned income	$ 39,565,471	$ 39,196,485	$ 35,280,547
Total loans, net of unearned income, percentage	100.00%	100.00%	100.00%
Commercial
Loans [Line Items]
Total loans, net of unearned income	$ 12,576,985	$ 12,549,164	$ 11,583,963
Total loans, net of unearned income, percentage	32.00%	32.00%	33.00%
Commercial real estate
Loans [Line Items]
Total loans, net of unearned income	$ 10,239,078	$ 9,950,947	$ 9,235,074
Total loans, net of unearned income, percentage	26.00%	25.00%	26.00%
Home equity
Loans [Line Items]
Total loans, net of unearned income	$ 337,016	$ 332,698	$ 321,435
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	$ 2,505,545	$ 2,372,383	$ 1,799,985
Total loans, net of unearned income, percentage	6.00%	6.00%	5.00%
Premium finance receivables | Property and casualty insurance
Loans [Line Items]
Total loans, net of unearned income	$ 5,738,880	$ 5,849,459	$ 4,937,408
Total loans, net of unearned income, percentage	14.00%	15.00%	14.00%
Premium finance receivables | Life insurance
Loans [Line Items]
Total loans, net of unearned income	$ 8,125,802	$ 8,090,998	$ 7,354,163
Total loans, net of unearned income, percentage	21.00%	21.00%	21.00%
Consumer and other
Loans [Line Items]
Total loans, net of unearned income	$ 42,165	$ 50,836	$ 48,519
Total loans, net of unearned income, percentage	0.00%	0.00%	0.00%