| Document And Entity Information | Sep. 25, 2019 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Sep. 25, 2019 |
| Entity Registrant Name | BEACON ROOFING SUPPLY INC |
| Entity Central Index Key | 0001124941 |
| Entity Emerging Growth Company | false |
| Entity File Number | 000-50924 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 36-4173371 |
| Entity Address, Address Line One | 505 Huntmar Park Drive |
| Entity Address, Address Line Two | Suite 300 |
| Entity Address, City or Town | Herndon |
| Entity Address, State or Province | VA |
| Entity Address, Postal Zip Code | 20170 |
| City Area Code | 571 |
| Local Phone Number | 323-3939 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $0.01 par value |
| Trading Symbol | BECN |
| Security Exchange Name | NASDAQ |
