Loans (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net deferred loan origination fees and costs	$ 4,100	$ 4,100	$ 5,400
Loans	16,076,945	$ 16,076,945	15,326,147
Time period for non-payment of loans that are placed on non-accrual status		90 days
Days past due for nonaccrual status credit card loans		120 days
Acquired Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Outstanding balance, including contractual principal, interest, fees and penalties, of all purchased loans	406,000	$ 406,000	590,900
Net reclassifications from nonaccretable to accretable, Accretable Yield		37,245	45,824
Covered impaired loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net reclassifications from nonaccretable to accretable, Accretable Yield	4,818		16,841
FDIC acquired loans covered by loss share agreement	323,700	323,700	$ 451,200
George Washington and Midwest Acquisitions | Non-Single Family Loss Share Agreement
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	129,100	129,100
George Washington and Midwest Acquisitions | Single Family Loss Share Agreement
Accounts, Notes, Loans and Financing Receivable [Line Items]
FDIC acquired loans covered by loss share agreement	$ 76,300	$ 76,300