Loans (Summary of Loan Portfolio) (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Loans [Line Items]
Total loans, net of unearned income	$ 37,053,103	$ 34,789,104	$ 32,911,187
Total loans, net of unearned income, percentage	100.00%	100.00%	100.00%
Commercial
Loans [Line Items]
Total loans, net of unearned income	$ 12,047,105	$ 11,904,068	$ 11,442,276
Total loans, net of unearned income, percentage	32.00%	34.00%	35.00%
Commercial real estate
Loans [Line Items]
Total loans, net of unearned income	$ 9,407,205	$ 8,990,286	$ 8,678,369
Total loans, net of unearned income, percentage	25.00%	26.00%	26.00%
Home equity
Loans [Line Items]
Total loans, net of unearned income	$ 325,826	$ 335,155	$ 369,806
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	$ 2,078,907	$ 1,637,099	$ 1,530,285
Total loans, net of unearned income, percentage	6.00%	5.00%	5.00%
Premium finance receivables | Property and casualty insurance
Loans [Line Items]
Total loans, net of unearned income	$ 5,541,447	$ 4,855,487	$ 4,521,871
Total loans, net of unearned income, percentage	15.00%	14.00%	14.00%
Premium finance receivables | Life insurance
Loans [Line Items]
Total loans, net of unearned income	$ 7,608,433	$ 7,042,810	$ 6,359,556
Total loans, net of unearned income, percentage	21.00%	20.00%	19.00%
Consumer and other
Loans [Line Items]
Total loans, net of unearned income	$ 44,180	$ 24,199	$ 9,024
Total loans, net of unearned income, percentage	0.00%	0.00%	0.00%