| Cover | May 11, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | May 11, 2021 |
| Entity Registrant Name | Semrush Holdings, Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-40276 |
| Entity Tax Identification Number | 84-4053265 |
| Entity Address, Address Line One | 800 Boylston Street |
| Entity Address, Address Line Two | Suite 2475 |
| Entity Address, City or Town | Boston |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02199 |
| City Area Code | 800 |
| Local Phone Number | 851-9959 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Class A Common Stock, par value $0.00001 per share |
| Trading Symbol | SEMR |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity Central Index Key | 0001831840 |
| Amendment Flag | false |
