Summary of Organization and Significant Accounting Policies - Prior Year Reclassifications (Details) - USD ($) $ in Thousands	12 Months Ended
Jan. 02, 2021	Dec. 28, 2019	Dec. 29, 2018
Reclassification [Line Items]
Transaction costs	$ 2,747	$ 2,222	$ 4,238
Gain on sale of property, plant and equipment	7,569	10,665	12,555
Summit Materials, LLC
Reclassification [Line Items]
Transaction costs	2,747	2,222	4,238
Gain on sale of property, plant and equipment	$ 7,569	10,665	12,555
Reclass From Separate Line Item To General And Administrative Expenses
Reclassification [Line Items]
Transaction costs		2,200	4,200
Reclass From Separate Line Item To General And Administrative Expenses \| Summit Materials, LLC
Reclassification [Line Items]
Transaction costs		2,200	4,200
Reclass From General And Administrative Expenses To Separate Line Item
Reclassification [Line Items]
Gain on sale of property, plant and equipment		10,700	12,600
Reclass From General And Administrative Expenses To Separate Line Item \| Summit Materials, LLC
Reclassification [Line Items]
Gain on sale of property, plant and equipment		$ 10,700	$ 12,600

This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 23
-URI http://asc.fasb.org/extlink&oid=116868678&loc=d3e1043-128460

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Amount of gain (loss) on sale or disposal of property, plant and equipment assets, including oil and gas property and timber property.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

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