| Cover Page | Nov. 04, 2021 | Aug. 12, 2021 |
| Cover [Abstract] | ||
| Document Type | 8-K | |
| Document Period End Date | Nov. 4, 2021 | |
| 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 | true | |
| Entity Ex Transition Period | false | |
| Entity Central Index Key | 0001726445 | |
| Document Fiscal Year Focus | 2021 | |
| Document Fiscal Period Focus | Q3 | |
| Amendment Flag | false |
