Loans and Allowance for Loan Losses (Loans, Net of Unearned Income) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Accounts Notes And Loans Receivable [Line Items]
Total loans	$ 21,035,952	$ 20,026,411	$ 19,543,717
Residential Mortgages [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	3,004,958	2,910,081	2,846,916
Consumer [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	2,152,325	2,147,867	2,122,528
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	3,060,568	2,341,779	2,311,699
Construction and Land Development [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	1,190,718	1,548,335	1,523,419
Total Commercial And Industrial [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	11,627,383	11,078,349	10,739,155
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	8,893,004	8,620,601	8,438,884
Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	$ 2,734,379	$ 2,457,748	$ 2,300,271