Loans and Leases (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Modifications, Recorded Investment	$ 164,561	$ 150,916
Federal Reserve Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	2,080,000
Loans held for sale	51,179	74,401
Proceeds from sale of all loans	823,457	874,788
Proceeds from sale of portfolio loans	162,649	77,665	$ 45,862
Proceeds from sale of loans held for sale	660,808	797,123	701,412
Loans and Leases Receivable, Collateral for Secured Borrowings	6,080,000	5,500,000
Advances from Federal Home Loan Banks	835,200	660,200
Federal Home Loan Bank Advances, Current Borrowing Capacity	5,240,000	4,840,000
Noncovered loans pledged to secure debt obligations	$ 8,750,000	8,260,000
Charge off of past due business credit card loans (days)	120 days
Loans and Leases Receivable, Gross, Carrying Amount, Covered	$ 67,800	84,800
Gain (Loss) on Sale of Loans and Leases	1,007	3,758	$ 0
Net deferred fees on non-PCI loans	1,700	6,700
Non-PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Accretion Income	13,600	14,300
PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Modifications, Recorded Investment	18,435	26,369
Nonaccruing	624	3,451
Loans on the Cost Recovery Method | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Carrying value of acquired impaired loans	300	500
Guaranty Bank
Financing Receivable, Recorded Investment [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Purchase Discount Remaining	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	2,700	4,200
Bancorporation
Financing Receivable, Recorded Investment [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Purchase Discount Remaining	18,100	27,400
Medical and Dental
Financing Receivable, Recorded Investment [Line Items]
Loans in the medical, dental or related field	$ 4,860,000	$ 4,660,000
Medical, dental or related fields percentage of total loans and leases	20.60%	21.50%
Federal Reserve Bank
Financing Receivable, Recorded Investment [Line Items]
Loans Pledged as Collateral	$ 2,770,000	$ 0