| Cover Page Document | 9 Months Ended |
| Jul. 04, 2020 | |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Aug. 12, 2020 |
| Entity Registrant Name | BLUE BIRD CORPORATION |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-36267 |
| Entity Tax Identification Number | 46-3891989 |
| Entity Address, Address Line One | 3920 Arkwright Road |
| Entity Address, Address Line Two | 2nd Floor |
| Entity Address, City or Town | Macon |
| Entity Address, State or Province | GA |
| Entity Address, Postal Zip Code | 31210 |
| City Area Code | 478 |
| Local Phone Number | 822-2801 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(g) Security | Common stock, $0.0001 par value |
| Trading Symbol | BLBD |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001589526 |
| Amendment Flag | false |
