Document and Entity Information Document - shares	3 Months Ended
	Mar. 31, 2020	May 01, 2020
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Document Transition Report	false
Commission File Number	1-07533
Name of Registrant	FEDERAL REALTY INVESTMENT TRUST
State of Organization	MD
IRS Employer Identification No.	52-0782497
Entity Address, Address	1626 East Jefferson Street
Entity Address, City	Rockville
Entity Address, State	MD
Entity Address, Zip Code	20852
Registrant's Telephone Area Code	301
Registrant's Telephone Number	998-8100
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		75,633,042
Entity Central Index Key	0000034903
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false
Common Shares of Beneficial Interest
Entity Information [Line Items]
Title of 12(b) Security	Common Shares of Beneficial Interest
Trading Symbol	FRT
Security Exchange Name	NYSE
5.0% Series C Cumulative Redeemable Preferred
Entity Information [Line Items]
Title of 12(b) Security	Depositary Shares, each representing 1/1000 of a share
Trading Symbol	FRT-C
Security Exchange Name	NYSE