DEBT - Schedule of Debt (Details) - USD ($) $ in Thousands	Oct. 02, 2021	Jan. 02, 2021
Debt Instrument [Line Items]
Total debt	$ 1,610,830	$ 1,915,425
Current portion of debt	6,354	6,354
Long-term debt	1,604,476	1,909,071
Gross amount	1,611,548
Debt discount	$ 718
5 1/8% Senior Notes, due 2025
Debt Instrument [Line Items]
Debt instrument interest rate (as a percent)	5.125%
Summit Materials, LLC
Debt Instrument [Line Items]
Total debt	$ 1,610,830	1,915,425
Current portion of debt	6,354	6,354
Long-term debt	1,604,476	1,909,071
Gross amount	1,611,548
Debt discount	$ 718
Summit Materials, LLC \| 5 1/8% Senior Notes, due 2025
Debt Instrument [Line Items]
Debt instrument interest rate (as a percent)	5.125%
Senior Notes \| Term Loan, due 2024
Debt Instrument [Line Items]
Total debt	$ 610,830	615,425
Gross amount	611,500	616,300
Debt discount	700	900
Senior Notes \| 5 1/8% Senior Notes, due 2025
Debt Instrument [Line Items]
Total debt	0	300,000
Senior Notes \| 6 1/2% Senior Notes, due 2027
Debt Instrument [Line Items]
Total debt	$ 300,000	300,000
Debt instrument interest rate (as a percent)	6.50%
Senior Notes \| 5 1/4% Senior Notes Due 2029
Debt Instrument [Line Items]
Total debt	$ 700,000	700,000
Debt instrument interest rate (as a percent)	5.25%
Senior Notes \| Summit Materials, LLC \| Term Loan, due 2024
Debt Instrument [Line Items]
Total debt	$ 610,830	615,425
Gross amount	611,500	616,300
Debt discount	700	900
Senior Notes \| Summit Materials, LLC \| 5 1/8% Senior Notes, due 2025
Debt Instrument [Line Items]
Total debt	0	300,000
Senior Notes \| Summit Materials, LLC \| 6 1/2% Senior Notes, due 2027
Debt Instrument [Line Items]
Total debt	$ 300,000	300,000
Debt instrument interest rate (as a percent)	6.50%
Senior Notes \| Summit Materials, LLC \| 5 1/4% Senior Notes Due 2029
Debt Instrument [Line Items]
Total debt	$ 700,000	$ 700,000
Debt instrument interest rate (as a percent)	5.25%

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, after accumulated amortization, of debt discount.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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