| Cover | Dec. 10, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K/A |
| Amendment Flag | true |
| Amendment Description | This Amendment No. 1 on Form 8-K/A amends the Current Report on Form 8-K filed on November 2, 2021 (the “Original Filing”) by Quanex Building Products Corporation (the “Company”). The Original Filing reported the appointment of Jason D. Lippert to the Company’s Board of Directors (the “Board”). At the time of the Original Filing, the Board had not made any determinations regarding committee assignments for Mr. Lippert. The Company hereby amends the Original Filing to include information on the committee assignments of Mr. Lippert in Item 5.02 below. Other than providing the additional information in Item 5.02 below, no other disclosure in the Original Filing is amended by this Form 8-K/A. |
| Document Period End Date | Dec. 10, 2021 |
| Entity File Number | 001-33913 |
| Entity Registrant Name | Quanex Building Products Corporation |
| Entity Central Index Key | 0001423221 |
| Entity Tax Identification Number | 26-1561397 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 1800 West Loop South |
| Entity Address, Address Line Two | Suite 1500 |
| Entity Address, City or Town | Houston |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 77027 |
| City Area Code | 713 |
| Local Phone Number | 961-4600 |
| 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 | NX |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
