Loans and Leases (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Threshold period past due for write-off of Business credit card loans (days)	120 days
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	$ 5,940,000		$ 5,940,000		$ 5,500,000
Advances from Federal Home Loan Banks	835,200		835,200		660,200
Federal Home Loan Bank Advances, Current Borrowing Capacity	5,100,000		5,100,000		4,840,000
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums	1,900		1,900		6,700
Loans and Leases Receivable, Gross, Carrying Amount, Covered	70,400		70,400		84,800
Federal Reserve Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	2,050,000		2,050,000
Loans held for sale	70,803		70,803		74,401
Carrying Value of Loans Held for Investment Sold	130,200		162,700
Transfer of Portfolio Loans and Leases to Held-for-sale			161,719	$ 0
Gain (Loss) on sale of loans and leases	800		1,007	3,758
Non-PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Nonaccruing	90,064		90,064		82,307
Accretion Income	4,200	$ 3,600	10,200	$ 9,700
PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Nonaccruing	1,000		1,000		3,500
Accretion Income	19,200	$ 17,200
Guaranty Bank
Financing Receivable, Recorded Investment [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Purchase Discount Remaining	15,600		15,600
Cordia Bancorp Inc.
Financing Receivable, Recorded Investment [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Purchase Discount Remaining	3,100		3,100		4,200
Bancorporation
Financing Receivable, Recorded Investment [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Purchase Discount Remaining	19,900		19,900		27,400
Federal Home Loan Bank of Atlanta
Financing Receivable, Recorded Investment [Line Items]
Loans Pledged as Collateral	8,610,000		8,610,000		$ 8,260,000
Federal Reserve Bank
Financing Receivable, Recorded Investment [Line Items]
Loans Pledged as Collateral	$ 2,740,000		$ 2,740,000