Off-Balance Sheet Credit Risk (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2015	Dec. 31, 2014
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
General settlement period of securities transactions	3 days
Fair value of securities accepted as collateral permitted to sell or repledge	$ 1,100.0	$ 1,200.0
Fair value of collateral securities sold or repledged	106.9	39.2
Outstanding commitments to originate loans	178.0	122.8
Letters of credit outstanding	10.2	10.4
Unused Lines Of Credit [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Unused lines of credit to commercial and consumer borrowers	$ 476.0	$ 368.7

General settlement period of securities transactions.

No definition available.

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- Definition

Outstanding commitments to originate loans.

+ References

No definition available.

+ Details

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- Definition

Unused lines of credit to commercial and consumer borrowers.

+ References

No definition available.

+ Details

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- Definition

Fair value as of the balance sheet date of customer securities accepted as collateral by the entity that it is permitted by contract or custom to sell or re-pledge to counterparties as collateral.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=55761124&loc=SL6224234-111729

+ Details

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- Definition

Fair value as of the balance sheet date of customer securities accepted as collateral by the entity that it has sold or re-pledged to counterparties as collateral.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=55761124&loc=SL6224234-111729

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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