v3.19.1
Document and Entity Information - shares
6 Months Ended
Apr. 30, 2019
Jun. 03, 2019
Document and Entity Information [Abstract]    
Entity Registrant Name QUANEX BUILDING PRODUCTS CORPORATION  
Entity Central Index Key 0001423221  
Trading Symbol NX  
Current Fiscal Year End Date --10-31  
Entity Filer Category Large Accelerated Filer  
Document Type 10-Q  
Document Period End Date Apr. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q2  
Amendment Flag false  
Entity Emerging Growth Company false  
Entity Small Business false  
Entity Common Stock, Shares Outstanding   33,121,513