SUMMARY OF ORGANIZATION AND SIGNIFICANT ACCOUNTING POLICIES - General Information (Details)	9 Months Ended
Oct. 02, 2021 segment cementPlant
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Number of operating segments	3
Number of reportable segments	3
Cement plant
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Number of plants \| cementPlant	2
Summit Materials, LLC
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Number of operating segments	3
Number of reportable segments	3
Summit Materials, LLC \| Cement plant
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Number of plants \| cementPlant	2

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8672-108599

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