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Document and Entity Information Document (USD $)
In Billions, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Feb. 09, 2012
Jun. 30, 2011
Entity Information [Line Items]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2011    
Document Fiscal Year Focus 2011    
Document Fiscal Period Focus FY    
Trading Symbol FRT    
Entity Registrant Name FEDERAL REALTY INVESTMENT TRUST    
Entity Central Index Key 0000034903    
Current Fiscal Year End Date --12-31    
Entity Filer Category Large Accelerated Filer    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 5.3
Entity Common Stock, Shares Outstanding   63,672,252