| Cover | Jun. 23, 2020 | Dec. 19, 2019 |
| Entity Information [Line Items] | ||
| Document Type | 8-K | |
| Document Period End Date | Jun. 23, 2020 | |
| Entity Registrant Name | FactSet Research Systems Inc. | |
| Entity Incorporation, State or Country Code | DE | |
| Entity File Number | 1-11869 | |
| Entity Tax Identification Number | 13-3362547 | |
| Entity Address, Address Line One | 45 Glover Avenue | |
| Entity Address, City or Town | Norwalk | |
| Entity Address, State or Province | CT | |
| Entity Address, Postal Zip Code | 06850 | |
| City Area Code | 203 | |
| Local Phone Number | 810-1000 | |
| Written Communications | false | |
| Soliciting Material | false | |
| Pre-commencement Tender Offer | false | |
| Pre-commencement Issuer Tender Offer | false | |
| Entity Emerging Growth Company | false | |
| Title of 12(b) Security | Common Stock, $0.01 Par Value | |
| Trading Symbol | FDS | |
| Entity Central Index Key | 0001013237 | |
| Amendment Flag | false | |
| New York Stock Exchange LLC | ||
| Entity Information [Line Items] | ||
| Security Exchange Name | NYSE | |
| The Nasdaq Stock Market | ||
| Entity Information [Line Items] | ||
| Security Exchange Name | NASDAQ |
