| Cover | Oct. 11, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Oct. 11, 2021 |
| Entity File Number | 001-39412 |
| Entity Registrant Name | FATHOM HOLDINGS INC. |
| Entity Central Index Key | 0001753162 |
| Entity Tax Identification Number | 82-1518164 |
| Entity Incorporation, State or Country Code | NC |
| Entity Address, Address Line One | 2000 Regency Parkway Drive |
| Entity Address, Address Line Two | Suite 300 |
| Entity Address, City or Town | Cary |
| Entity Address, State or Province | NC |
| Entity Address, Postal Zip Code | 27518 |
| City Area Code | 888 |
| Local Phone Number | 455-6040 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, No Par Value |
| Trading Symbol | FTHM |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | true |
