| Cover Page | Jan. 27, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jan. 27, 2021 |
| Entity Registrant Name | SOUND FINANCIAL BANCORP, INC. |
| Entity Incorporation, State or Country Code | MD |
| Entity File Number | 001-35633 |
| Entity Tax Identification Number | 45-5188530 |
| Entity Address, Address Line One | 2400 3rd Avenue, |
| Entity Address, Address Line Two | Suite 150, |
| Entity Address, City or Town | Seattle, |
| Entity Address, State or Province | WA |
| Entity Address, Postal Zip Code | 98121 |
| City Area Code | 206 |
| Local Phone Number | 448-0884 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.01 par value |
| Trading Symbol | SFBC |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001541119 |
| Amendment Flag | false |
