Loans (Summary of Loan Portfolio) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 21,640,797	$ 19,703,172
Covered loans	0	58,145
Total loans	$ 21,640,797	$ 19,761,317
Total loans, percentage	100.00%	100.00%
Covered loans, percentage	0.00%	0.00%
Percentage of Loans Net of Unearned Income Including Covered Loans	100.00%	100.00%
Commercial
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 6,787,677	$ 6,005,422
Total loans, percentage	31.00%	30.00%
Commercial real estate
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 6,580,618	$ 6,196,087
Total loans, percentage	30.00%	31.00%
Home equity
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 663,045	$ 725,793
Total loans, percentage	3.00%	4.00%
Residential real estate
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 832,120	$ 705,221
Total loans, percentage	4.00%	4.00%
Premium finance receivables | Commercial insurance loans
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 2,634,565	$ 2,478,581
Total loans, percentage	12.00%	12.00%
Premium finance receivables | Life insurance
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 4,035,059	$ 3,470,027
Total loans, percentage	19.00%	18.00%
Consumer and other
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 107,713	$ 122,041
Total loans, percentage	1.00%	1.00%