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Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | $ 343,018 us-gaap_AvailableForSaleSecurities | $ 257,770 us-gaap_AvailableForSaleSecurities
Equity Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 28 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember | 9,302 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember
Other Investments [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 11,748 us-gaap_AvailableForSaleSecurities / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherInvestmentsMember | 10,591 us-gaap_AvailableForSaleSecurities / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherInvestmentsMember
Fair Value, Measurements, Recurring [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 343,018 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | 257,770 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 331,242 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember | 237,877 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember
Fair Value, Measurements, Recurring [Member] | Other Investments [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 11,748 us-gaap_AvailableForSaleSecurities / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherInvestmentsMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | 10,591 us-gaap_AvailableForSaleSecurities / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherInvestmentsMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Equity Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 28 us-gaap_AvailableForSaleSecurities / us-gaap_EligibleItemOrGroupForFairValueOptionAxis = us-gaap_CommonStockMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember | 9,302 us-gaap_AvailableForSaleSecurities / us-gaap_EligibleItemOrGroupForFairValueOptionAxis = us-gaap_CommonStockMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember
Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 157,374 us-gaap_AvailableForSaleSecurities / us-gaap_EligibleItemOrGroupForFairValueOptionAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember | 150,375 us-gaap_AvailableForSaleSecurities / us-gaap_EligibleItemOrGroupForFairValueOptionAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember
Fair Value, Measurements, Recurring [Member] | U.S. Agency-Based Mortgage-Backed Securities [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 8,498 us-gaap_AvailableForSaleSecurities / us-gaap_EligibleItemOrGroupForFairValueOptionAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember | 7,074 us-gaap_AvailableForSaleSecurities / us-gaap_EligibleItemOrGroupForFairValueOptionAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 165,370 us-gaap_AvailableForSaleSecurities / us-gaap_EligibleItemOrGroupForFairValueOptionAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember | 80,428 us-gaap_AvailableForSaleSecurities / us-gaap_EligibleItemOrGroupForFairValueOptionAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 28 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | 9,302 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Equity Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 28 us-gaap_AvailableForSaleSecurities / us-gaap_EligibleItemOrGroupForFairValueOptionAxis = us-gaap_CommonStockMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember | 9,302 us-gaap_AvailableForSaleSecurities / us-gaap_EligibleItemOrGroupForFairValueOptionAxis = us-gaap_CommonStockMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 331,242 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | 237,877 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 331,242 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember | 237,877 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 157,374 us-gaap_AvailableForSaleSecurities / us-gaap_EligibleItemOrGroupForFairValueOptionAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember | 150,375 us-gaap_AvailableForSaleSecurities / us-gaap_EligibleItemOrGroupForFairValueOptionAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Agency-Based Mortgage-Backed Securities [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 8,498 us-gaap_AvailableForSaleSecurities / us-gaap_EligibleItemOrGroupForFairValueOptionAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember | 7,074 us-gaap_AvailableForSaleSecurities / us-gaap_EligibleItemOrGroupForFairValueOptionAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 165,370 us-gaap_AvailableForSaleSecurities / us-gaap_EligibleItemOrGroupForFairValueOptionAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember | 80,428 us-gaap_AvailableForSaleSecurities / us-gaap_EligibleItemOrGroupForFairValueOptionAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | 11,748 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | 10,591 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair value | $ 11,748 us-gaap_AvailableForSaleSecurities / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherInvestmentsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember | $ 10,591 us-gaap_AvailableForSaleSecurities / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherInvestmentsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember

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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 + Details
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