| Document and Entity Information | Feb. 11, 2021 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001023313 |
| Document Type | 8-K |
| Document Period End Date | Feb. 11, 2021 |
| Entity Registrant Name | FORRESTER RESEARCH, INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 000-21433 |
| Entity Tax Identification Number | 04-2797789 |
| Entity Address, Address Line One | 60 Acorn Park Drive |
| Entity Address, City or Town | Cambridge |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02140 |
| City Area Code | (617) |
| Local Phone Number | 613-6000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $.01 Par Value |
| Trading Symbol | FORR |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
