v3.10.0.1
Document and Entity Information Document - USD ($)
$ in Billions
12 Months Ended
Dec. 31, 2018
Feb. 08, 2019
Jun. 30, 2018
Document And Entity Information [Abstract]      
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    
Document Type 10-K    
Document Period End Date Dec. 31, 2018    
Document Fiscal Year Focus 2018    
Document Fiscal Period Focus FY    
Amendment Flag false    
Trading Symbol FRT    
Entity Common Stock, Shares Outstanding   74,365,801  
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     $ 9.3