Derivative Financial Instruments - Schedule of Derivative Financial Instruments on Statement of Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest Rate Contracts [Member]
Derivative [Line Items]
Derivatives in fair value hedging relationships	$ (1,047)	$ (522)	$ (298)
Interest Income/ (Expense) [Member]
Derivative [Line Items]
Derivatives in fair value hedging relationships	(1,047)	(522)	(298)
Interest Income/ (Expense) [Member] \| Interest Rate Contracts [Member]
Derivative [Line Items]
Derivatives in fair value hedging relationships	(1,047)	(522)	(298)
Other Income [Member] \| Interest Rate Contracts [Member]
Derivative [Line Items]
Derivative instruments not designated as hedging instruments, loss	0	0	0
Derivative instruments not designated as hedging instruments, net	$ 0	$ 0	$ 0

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5618551-113959

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (a),(c),(d),(e)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624171-113959

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- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624171-113959

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Amount of realized and unrealized loss of derivative instruments not designated or qualifying as hedging instruments.

+ References

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