v3.10.0.1
Document and Entity Information Document - shares
9 Months Ended
Sep. 30, 2018
Oct. 26, 2018
Document And Entity Information [Abstract]    
9/30/2018 Sep. 30, 2018  
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-Q  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q3  
Amendment Flag false  
Entity Emerging Growth Company false  
Entity Small Business false  
Entity Common Stock, Shares Outstanding   73,863,142