Document and Entity Information Document - shares	6 Months Ended
	Jun. 30, 2022	Aug. 01, 2022
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2022
Document Transition Report	false
Entity File Number	1-07533
Name of Registrant	FEDERAL REALTY INVESTMENT TRUST
Entity Central Index Key	0000034903
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q2
Amendment Flag	false
State of Organization	MD
IRS Employer Identification No.	87-3916363
Entity Address, Address	909 Rose Avenue, Suite 200
Entity Address, City	North Bethesda
Entity Address, State	MD
Entity Address, Zip Code	20852
City 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		80,908,184
Federal Realty OP LP
Entity Information [Line Items]
Entity File Number	333-262016-01
Name of Registrant	FEDERAL REALTY OP LP
State of Organization	DE
IRS Employer Identification No.	52-0782497
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
New York Stock Exchange | 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 | Depositary Shares
Entity Information [Line Items]
Title of 12(b) Security	Depositary Shares, each representing 1/1000 of a share of
Trading Symbol	FRT-C
Security Exchange Name	NYSE