Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Apr. 30, 2019	May 31, 2019	Oct. 31, 2018
Document and Entity Information
Entity Registrant Name	GMS Inc.
Entity Central Index Key	0001600438
Document Type	10-K
Document Period End Date	Apr. 30, 2019
Amendment Flag	false
Current Fiscal Year End Date	--04-30
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 548.2
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		40,374,750
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY