Loans and Allowance for Loan Losses (Loans, Net of Unearned Income) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 19,370,917	$ 19,004,163	$ 18,473,841
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,780,359	2,690,472	2,493,923
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,088,378	2,115,295	2,093,287
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,342,192	2,384,599	2,401,673
Construction and Land Development [Member] | Total Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,515,233	1,373,421	1,313,522
Total Commercial And Industrial [Member] | Total Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	10,644,755	10,440,376	10,171,436
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	8,410,961	8,297,937	8,093,104
Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 2,233,794	$ 2,142,439	$ 2,078,332