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Real Estate Partnerships (Narrative) (Details)
Mar. 31, 2015
project
Schedule of Equity Method Investments [Line Items]  
Number of real estate properties owned or had a majority interest in 90us-gaap_NumberOfRealEstateProperties
Federal Realty Investment Trust / ING Clarion Partners Partnership  
Schedule of Equity Method Investments [Line Items]  
Number of real estate properties owned or had a majority interest in 6us-gaap_NumberOfRealEstateProperties
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= frt_FederalLionVentureLpMember
Federal Realty Investment Trust | Federal Realty Investment Trust / ING Clarion Partners Partnership  
Schedule of Equity Method Investments [Line Items]  
Ownership interest in Partnership 30.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ dei_LegalEntityAxis
= frt_FederalRealtyInvestmentTrustMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= frt_FederalLionVentureLpMember
ING Clarion Partners | Federal Realty Investment Trust / ING Clarion Partners Partnership  
Schedule of Equity Method Investments [Line Items]  
Ownership interest in Partnership 70.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ dei_LegalEntityAxis
= frt_ClarionMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= frt_FederalLionVentureLpMember