Loans and Leases (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Threshold period past due for write-off of Business credit card loans (days)
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	$ 6,260,000		$ 6,080,000
Advances from Federal Home Loan Banks	85,200		835,200
Federal Home Loan Bank Advances, Current Borrowing Capacity	6,170,000		5,240,000
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums	1,500		1,700
Loans and Leases Receivable, Gross, Carrying Amount, Covered	65,500		67,800
Federal Reserve Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	2,160,000		2,080,000
Loans held for sale	46,660		51,179
Transfer of Portfolio Loans and Leases to Held-for-sale	0	$ 32,130
Proceeds From Sales of Loans	138,538	195,131
Proceeds from sales of portfolio loans	0	32,294
Gain (Loss) on sale of loans and leases	0	164
Non-PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Nonaccruing	89,260		92,534
Accretion Income	2,900	3,200
PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Nonaccruing	1,600		600
Accretion Income	18,000	$ 19,400
Guaranty Bank
Financing Receivable, Recorded Investment [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Purchase Discount Remaining	13,300		14,200
Cordia Bancorp Inc.
Financing Receivable, Recorded Investment [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Purchase Discount Remaining	2,500		2,700
Bancorporation
Financing Receivable, Recorded Investment [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Purchase Discount Remaining	16,400		18,100
Federal Home Loan Bank of Atlanta
Financing Receivable, Recorded Investment [Line Items]
Loans Pledged as Collateral	9,110,000		8,750,000
Federal Reserve Bank
Financing Receivable, Recorded Investment [Line Items]
Loans Pledged as Collateral	$ 2,860,000		$ 2,770,000