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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 | $ 2,243,000 us-gaap_ImpairedFinancingReceivableRecordedInvestment | $ 1,843,000 us-gaap_ImpairedFinancingReceivableRecordedInvestment | $ 2,059,000 us-gaap_ImpairedFinancingReceivableRecordedInvestment
Specific allocation for impaired loans | 428,000 us-gaap_ImpairedFinancingReceivableRelatedAllowance | 387,000 us-gaap_ImpairedFinancingReceivableRelatedAllowance | 261,000 us-gaap_ImpairedFinancingReceivableRelatedAllowance
Asset impairment charges | 0 us-gaap_AssetImpairmentCharges | 0 us-gaap_AssetImpairmentCharges |
Level 3 [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Impaired loans categorized as Level 3 | 1,800,000 us-gaap_ImpairedFinancingReceivableRecordedInvestment / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 1,400,000 us-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 | $ 427,000 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | $ 387,000 us-gaap_ImpairedFinancingReceivableRelatedAllowance / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |

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