Loans (Summary of Loan Portfolio) (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Loans [Line Items]
Total loans, net of unearned income	$ 38,167,613	$ 34,789,104	$ 33,264,043
Total loans, net of unearned income, percentage	100.00%	100.00%	100.00%
Commercial
Loans [Line Items]
Total loans, net of unearned income	$ 12,259,250	$ 11,904,068	$ 11,187,972
Total loans, net of unearned income, percentage	32.00%	34.00%	33.00%
Commercial real estate
Loans [Line Items]
Total loans, net of unearned income	$ 9,578,184	$ 8,990,286	$ 8,885,714
Total loans, net of unearned income, percentage	25.00%	26.00%	27.00%
Home equity
Loans [Line Items]
Total loans, net of unearned income	$ 328,822	$ 335,155	$ 347,662
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	$ 2,235,459	$ 1,637,099	$ 1,547,736
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	$ 5,713,340	$ 4,855,487	$ 4,616,977
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	$ 8,004,856	$ 7,042,810	$ 6,655,453
Total loans, net of unearned income, percentage	21.00%	20.00%	20.00%
Consumer and other
Loans [Line Items]
Total loans, net of unearned income	$ 47,702	$ 24,199	$ 22,529
Total loans, net of unearned income, percentage	0.00%	0.00%	0.00%