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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) - 10K
 12 Months Ended
Dec. 31, 2014
company
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES  
Number of insurance companies through which the entity conducts operations 4rli_NumberOfInsuranceCompaniesThroughWhichOperationsConducted
RLI Ins.  
DESCRIPTION OF BUSINESS  
Number of states in which entity operates 50us-gaap_NumberOfStatesInWhichEntityOperates
/ dei_LegalEntityAxis
= rli_RLIInsuranceCompanyMember
Mt. Hawley Insurance Company  
DESCRIPTION OF BUSINESS  
Number of states in which entity operates 50us-gaap_NumberOfStatesInWhichEntityOperates
/ dei_LegalEntityAxis
= rli_HawleyInsuranceCompanyMember
RIC  
DESCRIPTION OF BUSINESS  
Number of states in which entity operates 48us-gaap_NumberOfStatesInWhichEntityOperates
/ dei_LegalEntityAxis
= rli_RLIIndemnityCompanyMember
Contractors Bonding and Insurance Company  
DESCRIPTION OF BUSINESS  
Number of states in which entity operates 50us-gaap_NumberOfStatesInWhichEntityOperates
/ dei_LegalEntityAxis
= rli_ContractorsBondingAndInsuranceCompanyMember