| Cover Page | Feb. 28, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Feb. 28, 2022 |
| Entity Registrant Name | Seer, Inc. |
| Entity File Number | 001-39747 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 82-1153150 |
| Entity Address, Address Line One | 3800 Bridge Parkway |
| Entity Address, Address Line Two | Suite 102 |
| Entity Address, City or Town | Redwood City |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94065 |
| City Area Code | 650 |
| Local Phone Number | 453-0000 |
| 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 | SEER |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001726445 |
| Document Fiscal Year Focus | |
| Document Fiscal Period Focus | |
| Amendment Flag | false |
