Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended	48 Months Ended
	Dec. 31, 2012	Dec. 31, 2012 transaction	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Number of transactions with the federal deposit insurance corporation to acquire failed banks		4
Required reserves on deposits maintained	$ 16.5	$ 16.5	$ 16.6
Finite-lived intangible assets useful life	10 years
Furniture, Fixtures and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	3 years
Furniture, Fixtures and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	10 years
Building and Building Improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	10 years
Building and Building Improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	40 years
Software [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	3 years
Core Deposits [Member]
Property, Plant and Equipment [Line Items]
Finite-lived intangible assets useful life	10 years
State and Local Jurisdiction [Member]
Property, Plant and Equipment [Line Items]
Right to receive state tax credit at agreed upon rates	10 years