Document and Entity Information - shares	3 Months Ended
	Jan. 31, 2020	Mar. 03, 2020
Class of Stock [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jan. 31, 2020
Document Transition Report	false
Entity File Number	1-33913
Entity Registrant Name	QUANEX BUILDING PRODUCTS CORPORATION
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-1561397
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
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	NX
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Shell Company	false
Entity Central Index Key	0001423221
Current Fiscal Year End Date	--10-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		32,947,975