Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Dec. 31, 2012
Commitment To Extend Credit and Unused Lines of Credit [Member]
Guarantor Obligations [Line Items]
Commitments - maximum potential obligation	$ 1,100.0	$ 841.7
Standby Letters of Credit [Member]
Guarantor Obligations [Line Items]
Commitments - maximum potential obligation	45.0	37.5
Obligation instrument term	P5Y
Commercial Letters of Credit [Member]
Guarantor Obligations [Line Items]
Commitments - maximum potential obligation	$ 37.4	$ 16.6

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Interpretation (FIN)

-Number 45

-Paragraph 13

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (b)(1)

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

Name:	us-gaap_GuaranteeObligationsMaximumExposure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant