Loans and Allowance for Loan Losses (Loans, Net of Unearned Income) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Accounts Notes And Loans Receivable [Line Items]
Total loans	$ 20,112,838	$ 20,026,411	$ 19,092,504
Residential Mortgages [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	2,933,251	2,910,081	2,732,821
Consumer [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	2,104,372	2,147,867	2,029,178
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	2,563,394	2,341,779	2,394,862
Construction and Land Development [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	1,340,067	1,548,335	1,413,878
Total Commercial And Industrial [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	11,171,754	11,078,349	10,521,765
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	8,656,326	8,620,601	8,336,222
Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	$ 2,515,428	$ 2,457,748	$ 2,185,543