Document and Entity Information - USD ($)	12 Months Ended
	Dec. 30, 2017	Feb. 07, 2018	Jul. 01, 2017
Document Information [Line Items]
Entity Registrant Name	Summit Materials, Inc.
Entity Central Index Key	0001621563
Document Type	10-K
Document Period End Date	Dec. 30, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-30
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Public Float			$ 3,100,000,000
Membership interests description	As of February 7, 2018, 100% of Summit Materials, LLC's outstanding limited liability company interests were held by Summit Materials Intermediate Holdings, LLC, its sole member and an indirect subsidiary of Summit Materials, Inc
Common Class A
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		110,365,594
Common Class B
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		100
Summit Materials, LLC
Document Information [Line Items]
Entity Registrant Name	Summit Materials, LLC
Entity Central Index Key	0001571371
Document Type	10-K
Document Period End Date	Dec. 30, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Public Float	$ 0
Membership interests percentage	100.00%