Loans (Summary of Loan Portfolio) (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Loans [Line Items]
Total loans, net of unearned income	$ 31,402,903	$ 26,800,290	$ 25,304,659
Total loans, net of unearned income, percentage	100.00%	100.00%	100.00%
Commercial
Loans [Line Items]
Total loans, net of unearned income	$ 11,859,232	$ 8,285,920	$ 8,270,774
Total loans, net of unearned income, percentage	38.00%	31.00%	33.00%
Commercial real estate
Loans [Line Items]
Total loans, net of unearned income	$ 8,200,745	$ 8,020,276	$ 7,276,244
Total loans, net of unearned income, percentage	26.00%	30.00%	29.00%
Home equity
Loans [Line Items]
Total loans, net of unearned income	$ 466,596	$ 513,066	$ 527,370
Total loans, net of unearned income, percentage	1.00%	2.00%	2.00%
Residential real estate
Loans [Line Items]
Total loans, net of unearned income	$ 1,427,429	$ 1,354,221	$ 1,118,178
Total loans, net of unearned income, percentage	5.00%	5.00%	4.00%
Premium finance receivables | Commercial insurance loans
Loans [Line Items]
Total loans, net of unearned income	$ 3,999,774	$ 3,442,027	$ 3,368,423
Total loans, net of unearned income, percentage	13.00%	13.00%	13.00%
Premium finance receivables | Life insurance
Loans [Line Items]
Total loans, net of unearned income	$ 5,400,802	$ 5,074,602	$ 4,634,478
Total loans, net of unearned income, percentage	17.00%	19.00%	18.00%
Consumer and other
Loans [Line Items]
Total loans, net of unearned income	$ 48,325	$ 110,178	$ 109,192
Total loans, net of unearned income, percentage	0.00%	0.00%	1.00%