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Indemnity Capital Stock (Details) (Indemnity)
3 Months Ended 12 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Class A
   
Common Stock    
Class A common stock shares issued upon conversion of Class B common stock shares (in shares) 0us-gaap_ConversionOfStockSharesIssued1
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
0us-gaap_ConversionOfStockSharesIssued1
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
Class B
   
Common Stock    
Ratio for converting shares of Class B common stock into shares of Class A common stock (as a percent) 2400.00%erie_CommonStockConversionRatio
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
2400.00%erie_CommonStockConversionRatio
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
Class B common stock shares converted into Class A common stock shares (in shares) 0us-gaap_ConversionOfStockSharesConverted1
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
0us-gaap_ConversionOfStockSharesConverted1
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember