| Cover Page | 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 | May 5, 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 |
