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Fair Value of Instruments - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest-bearing deposits maturing date	90 days
Carrying amounts of dividends payable, number of days	Forty days
Impaired loans categorized as Level 3	$ 2,243,000us-gaap_ImpairedFinancingReceivableRecordedInvestment	$ 1,843,000us-gaap_ImpairedFinancingReceivableRecordedInvestment	$ 2,059,000us-gaap_ImpairedFinancingReceivableRecordedInvestment
Specific allocation for impaired loans	428,000us-gaap_ImpairedFinancingReceivableRelatedAllowance	387,000us-gaap_ImpairedFinancingReceivableRelatedAllowance	261,000us-gaap_ImpairedFinancingReceivableRelatedAllowance
Asset impairment charges	0us-gaap_AssetImpairmentCharges	0us-gaap_AssetImpairmentCharges
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans categorized as Level 3	1,800,000us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member	1,400,000us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Fair Value on a Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Specific allocation for impaired loans	$ 427,000us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember	$ 387,000us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember

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- Definition

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585



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-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 45

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-URI http://asc.fasb.org/extlink&oid=8077374&loc=d3e2420-110228

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- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 14A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953550-111524

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (a)(3)

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