| Cover Page | Aug. 03, 2021 | May 05, 2021 |
| Entity Information [Line Items] | ||
| Entity Address, Address Line One | 909 Rose Avenue, Suite 200 | |
| Entity Address, City or Town | North Bethesda, | |
| Entity Address, State or Province | MD | |
| Entity Address, Postal Zip Code | 20852 | |
| Entity Emerging Growth Company | false | |
| Pre-commencement Issuer Tender Offer | false | |
| Pre-commencement Tender Offer | false | |
| Soliciting Material | false | |
| Written Communications | false | |
| Entity Incorporation, State or Country Code | MD | |
| Document Type | 8-K | |
| Entity Central Index Key | 0000034903 | |
| Amendment Flag | false | |
| Document Period End Date | Aug. 3, 2021 | |
| Entity Registrant Name | Federal Realty Investment Trust | |
| Entity File Number | 1-07533 | |
| Entity Tax Identification Number | 52-0782497 | |
| City Area Code | 301 | |
| Local Phone Number | 998-8100 | |
| 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 | |
| Depository 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 |
