SUMMARY OF ORGANIZATION AND SIGNIFICANT ACCOUNTING POLICIES - General Information (Details)	3 Months Ended
	Mar. 28, 2020 segment plant
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 | plant	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 | plant	2