| Document and Entity Information | Mar. 16, 2022 |
| Document and Entity Information [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Mar. 16, 2022 |
| Entity File Number | 001-16501 |
| Entity Registrant Name | Williams Industrial Services Group Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 73-1541378 |
| Entity Address, Address Line One | 200 Ashford Center North |
| Entity Address, Adress Line Two | Suite 425 |
| Entity Address, City or Town | Atlanta |
| Entity Address, State or Province | GA |
| Entity Address, Postal Zip Code | 30338 |
| City Area Code | 770 |
| Local Phone Number | 879-4400 |
| 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 $0.01 per share |
| Trading Symbol | WLMS |
| Security Exchange Name | NYSEAMER |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001136294 |
| Amendment Flag | false |
