| Cover | Nov. 06, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Nov. 6, 2020 |
| Entity File Number | 001-37784 |
| Entity Registrant Name | GMS INC. |
| Entity Central Index Key | 0001600438 |
| Entity Tax Identification Number | 46-2931287 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 100 Crescent Centre Parkway |
| Entity Address, Address Line Two | Suite 800 |
| Entity Address, City or Town | Tucker |
| Entity Address, State or Province | GA |
| Entity Address, Postal Zip Code | 30084 |
| City Area Code | 800 |
| Local Phone Number | 392-4619 |
| 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 | GMS |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
