Loans and Allowance for Credit Losses (Loans, Net of Unearned Income) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accounts Notes And Loans Receivable [Line Items]
Total loans	$ 21,212,755	$ 20,026,411
Residential Mortgages [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	2,990,631	2,910,081
Consumer [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	2,164,818	2,147,867
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	2,994,448	2,341,779
Construction and Land Development [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	1,157,451	1,548,335
Total Commercial And Industrial [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	11,905,407	11,078,349
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	9,166,947	8,620,601
Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	$ 2,738,460	$ 2,457,748