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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName EATON VANCE SPECIAL INVESTMENT TRUST
Central Index Key dei_EntityCentralIndexKey 0000031266
Document Creation Date dei_DocumentCreationDate Aug. 25, 2016
Document Effective Date dei_DocumentEffectiveDate Aug. 25, 2016
Prospectus Date rr_ProspectusDate Aug. 01, 2016