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Debt - Schedule of Debt (Details) - USD ($)	Jan. 02, 2021	Dec. 28, 2019	Jun. 01, 2017
Debt
Total debt	$ 1,915,425,000	$ 1,872,273,000
Current portion of long-term debt	6,354,000	7,942,000
Long-term Debt, Excluding Current Maturities	1,909,071,000	1,864,331,000
Gross amount	1,916,314,000
Debt discount	889,000
Summit Materials, LLC
Debt
Total debt	1,915,425,000	1,872,273,000
Current portion of long-term debt	6,354,000	7,942,000
Long-term Debt, Excluding Current Maturities	1,909,071,000	1,864,331,000
Gross amount	1,916,314,000
Debt discount	889,000
Term Loan, due 2024:
Debt
Total debt	615,425,000	623,140,000
Gross amount	616,300,000	624,300,000
Debt discount	900,000	1,100,000
Term Loan, due 2024: \| Summit Materials, LLC
Debt
Total debt	615,425,000	623,140,000
Gross amount	616,300,000	624,300,000
Debt discount	900,000	1,100,000
6 1⁄8% Senior Notes, due 2023:
Debt
Total debt	$ 0	649,133,000
Debt instrument interest rate (as a percent)	6.125%
Gross amount		650,000,000.0
Debt discount		900,000
6 1⁄8% Senior Notes, due 2023: \| Summit Materials, LLC
Debt
Total debt	$ 0	649,133,000
Debt instrument interest rate (as a percent)	6.125%
Gross amount		650,000,000.0
Debt discount		900,000
5 1⁄8% Senior Notes, due 2025
Debt
Total debt	$ 300,000,000	300,000,000
5 1⁄8% Senior Notes, due 2025 \| Summit Materials, LLC
Debt
Total debt	$ 300,000,000	300,000,000	$ 300,000,000.0
Debt instrument interest rate (as a percent)	5.125%		5.125%
Senior Notes \| 6 1⁄2% Senior Notes, due 2027
Debt
Total debt	$ 300,000,000	300,000,000
Debt instrument interest rate (as a percent)	6.50%
Senior Notes \| 6 1⁄2% Senior Notes, due 2027 \| Summit Materials, LLC
Debt
Total debt	$ 300,000,000	300,000,000
Debt instrument interest rate (as a percent)	6.50%
Senior Notes \| 5 1⁄4% Senior Notes, due 2029
Debt
Total debt	$ 700,000,000	0
Debt instrument interest rate (as a percent)	5.25%
Senior Notes \| 5 1⁄4% Senior Notes, due 2029 \| Summit Materials, LLC
Debt
Total debt	$ 700,000,000	$ 0
Debt instrument interest rate (as a percent)	5.25%