Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

+ Details

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Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The aggregate fair value of assets needed to immediately settle the derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4H

-Subparagraph (f)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624258-113959

+ Details

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Period Type:	instant

- Definition

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4H

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624258-113959

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- Definition

High end period remaining until maturity for the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

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Period Type:	duration

- Definition

Low end period remaining until maturity of derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of derivative instruments of a particular group held by the entity.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5580258-113959

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1A

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5579245-113959

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- Details

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Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013 Swap	Mar. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Termination value of derivatives in a net liability position	9.9
Minimum collateral with counterparties	10.0
Not Designated as Hedging Instrument \| Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Number of interest rate swaps	44	28
Derivative, Notional Amount	251.9	150.3
Not Designated as Hedging Instrument \| Residential Mortgage Loan Commitments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Notional Amount	3.8	7.1
Not Designated as Hedging Instrument \| Credit Risk Contract
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Notional Amount	13.4		13.4
Not Designated as Hedging Instrument \| Minimum
Derivative Instruments, Gain (Loss) [Line Items]
Number of days for commitments to expire, lower limit	30 days
Not Designated as Hedging Instrument \| Maximum
Derivative Instruments, Gain (Loss) [Line Items]
Number of days for commitments to expire, higher limit	60 days
Cash Flow Hedging \| Designated as Hedging Instrument \| Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Number of interest rate swaps	1
Derivative, Notional Amount	150.0		$ 150.0