Loans (Summary of Loan Portfolio) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Loans [Line Items]
Loans, net of unearned income	$ 23,820,691	$ 21,640,797
Total loans, percentage	100.00%	100.00%
Commercial
Loans [Line Items]
Loans, net of unearned income	$ 7,828,538	$ 6,787,677
Total loans, percentage	33.00%	31.00%
Commercial real estate
Loans [Line Items]
Loans, net of unearned income	$ 6,933,252	$ 6,580,618
Total loans, percentage	29.00%	30.00%
Home equity
Loans [Line Items]
Loans, net of unearned income	$ 552,343	$ 663,045
Total loans, percentage	2.00%	3.00%
Residential real estate
Loans [Line Items]
Loans, net of unearned income	$ 1,002,464	$ 832,120
Total loans, percentage	4.00%	4.00%
Premium finance receivables | Commercial
Loans [Line Items]
Loans, net of unearned income	$ 2,841,659	$ 2,634,565
Total loans, percentage	12.00%	12.00%
Premium finance receivables | Life insurance
Loans [Line Items]
Loans, net of unearned income	$ 4,541,794	$ 4,035,059
Total loans, percentage	19.00%	19.00%
Consumer and other
Loans [Line Items]
Loans, net of unearned income	$ 120,641	$ 107,713
Total loans, percentage	1.00%	1.00%