Loans and Allowance for Loan Losses (Loans, Net of Unearned Income) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 18,204,868	$ 16,752,151	$ 15,978,124
Total Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	13,879,509	12,545,507
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,266,263	2,146,713	2,000,967
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,059,096	2,059,931	2,060,245
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,505,104	2,013,890	1,752,745
Construction and Land Development [Member] | Total Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,252,667	1,010,879	1,095,414
Total Commercial & Industrial [Member] | Total Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	10,121,738	9,520,738	9,068,753
Total Commercial & Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	8,074,287	7,613,917	7,145,406
Total Commercial & Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 2,047,451	$ 1,906,821	$ 1,923,347