| Cover Page | Jul. 31, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jul. 31, 2020 |
| Entity Registrant Name | Synalloy Corporation |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 0-19687 |
| Entity Tax Identification Number | 57-0426694 |
| Entity Address, Address Line One | 4510 Cox Road, |
| Entity Address, Address Line Two | Suite 201, |
| Entity Address, City or Town | Richmond, |
| Entity Address, State or Province | VA |
| Entity Address, Postal Zip Code | 23060 |
| City Area Code | (804) |
| Local Phone Number | 822-3260 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $1.00 per share |
| Trading Symbol | SYNL |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000095953 |
| Amendment Flag | false |
