Summary of Significant Accounting Policies Significant Accounting Policies (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Locations
Derivative [Line Items]
Locations | Locations	330
Federal Reserve Bank Reserve Requirement	$ 126.1
Cash Held at Federal Reserve Bank	$ 30.6
Amortization period of annual fees on credit card loans, months	12 months
Period past due loans are placed on non-accrual, days	90 days
Consumer loans charged down to fair value, days delinquent	120 days
Period past due credit card loans are charged off, days	180 days
Common stock dividend rate percentage	5.00%
Swaps with Central Clearing Agency [Member] | Cash [Member]
Derivative [Line Items]
Value Of Collateral Posted	$ 12.5