Cover Page - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2019	Feb. 05, 2020	Jun. 30, 2019
Entity Information [Line Items]
Document Annual Report	true
Document Transition Report	false
Entity Incorporation, State or Country Code	MD
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, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		75,651,842
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			$ 9.7
Entity File Number	1-07533
Entity Tax Identification Number	52-0782497
Entity Address, Address Line One	1626 East Jefferson Street
Entity Address, City or Town	Rockville
Entity Address, State or Province	MD
Entity Address, Postal Zip Code	20852
City Area Code	301)
Local Phone Number	998-8100
Entity Interactive Data Current	Yes
New York Stock Exchange, Inc. | 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
New York Stock Exchange, Inc. | Depositary Shares
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