Employee Benefit Plans - Estimated Benefit Payments (Detail) $ in Thousands	Jan. 02, 2021 USD ($)
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2021	$ 1,692
2022	1,693
2023	1,696
2024	1,655
2025	1,613
2026 - 2030	7,597
Pension Benefits \| Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2021	1,692
2022	1,693
2023	1,696
2024	1,655
2025	1,613
2026 - 2030	7,597
Healthcare & Life Ins
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2021	636
2022	630
2023	617
2024	619
2025	627
2026 - 2030	3,139
Healthcare & Life Ins \| Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2021	636
2022	630
2023	617
2024	619
2025	627
2026 - 2030	$ 3,139

Amount of benefit for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following current fiscal year.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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Amount of benefit for defined benefit plan expected to be paid in next fiscal year following current fiscal year.

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Amount of benefit for defined benefit plan expected to be paid in fifth fiscal year following current fiscal year.

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Amount of benefit for defined benefit plan expected to be paid in fourth fiscal year following current fiscal year.

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Amount of benefit for defined benefit plan expected to be paid in third fiscal year following current fiscal year.

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Amount of benefit for defined benefit plan expected to be paid in second fiscal year following current fiscal year.

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