Goodwill - Summary of Goodwill by Reportable Segments (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 30, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Beginning balance	$ 782,212	$ 596,397
Acquisitions	249,958	184,490
Foreign currency translation adjustments	4,150	1,325
Ending balance	1,036,320	782,212
Summit Materials, LLC
Goodwill [Roll Forward]
Beginning balance	782,212	596,397
Acquisitions	250,958	184,490
Foreign currency translation adjustments	4,150	1,325
Ending balance	1,037,320	782,212
West
Goodwill [Roll Forward]
Beginning balance	334,257	303,926
Acquisitions	187,883	29,006
Foreign currency translation adjustments	4,150	1,325
Ending balance	526,290	334,257
West \| Summit Materials, LLC
Goodwill [Roll Forward]
Beginning balance	334,257	303,926
Acquisitions	188,883	29,006
Foreign currency translation adjustments	4,150	1,325
Ending balance	527,290	334,257
East
Goodwill [Roll Forward]
Beginning balance	243,417	98,308
Acquisitions	61,957	145,109
Ending balance	305,374	243,417
East \| Summit Materials, LLC
Goodwill [Roll Forward]
Beginning balance	243,417	98,308
Acquisitions	61,957	145,109
Ending balance	305,374	243,417
Cement
Goodwill [Roll Forward]
Beginning balance	204,538	194,163
Acquisitions	118	10,375
Ending balance	204,656	204,538
Cement \| Summit Materials, LLC
Goodwill [Roll Forward]
Beginning balance	204,538	194,163
Acquisitions	118	10,375
Ending balance	$ 204,656	$ 204,538

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=64834752&loc=SL49117168-202975

+ Details

Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

+ Details

Name:	us-gaap_GoodwillAcquiredDuringPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

+ Details

Name:	us-gaap_GoodwillForeignCurrencyTranslationGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_GoodwillRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=sum_SummitMaterialsLlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=sum_WestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=sum_EastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=sum_CementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: