COMMITMENTS AND CONTINGENCIES - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 28, 2020	Dec. 28, 2019
Loss Contingencies [Line Items]
Term of purchase commitments	1 year
Site Restoration Obligations
Loss Contingencies [Line Items]
Anticipated costs	$ 96.7	$ 97.4
Site Restoration Obligations \| Other noncurrent liabilities
Loss Contingencies [Line Items]
Site restoration obligation, non-current	31.5	28.8
Site Restoration Obligations \| Accrued expenses.
Loss Contingencies [Line Items]
Asset retirement obligation, current	$ 5.0	7.9
Summit Materials, LLC
Loss Contingencies [Line Items]
Term of purchase commitments	1 year
Summit Materials, LLC \| Site Restoration Obligations
Loss Contingencies [Line Items]
Anticipated costs	$ 96.7	97.4
Summit Materials, LLC \| Site Restoration Obligations \| Other noncurrent liabilities
Loss Contingencies [Line Items]
Site restoration obligation, non-current	31.5	28.8
Summit Materials, LLC \| Site Restoration Obligations \| Accrued expenses.
Loss Contingencies [Line Items]
Asset retirement obligation, current	$ 5.0	$ 7.9

Total undiscounted anticipated costs for asset retirement obligations.

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- Definition

Term of purchase commitment, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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- Definition

Current portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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Noncurrent portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

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+ References

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