Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Sep. 30, 2017	Dec. 30, 2017
Contingencies
Term of purchase commitments		1 year
Assumption of Obligations Under Indemnification Agreement
Contingencies
Settlement amount	$ 3.5
Reduction of accrual due to settlement	0.8
Summit Materials, LLC
Contingencies
Term of purchase commitments		1 year
Summit Materials, LLC \| Assumption of Obligations Under Indemnification Agreement
Contingencies
Settlement amount	3.5
Reduction of accrual due to settlement	$ 0.8

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

No definition available.

+ Details

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- Definition

Amount of judgment or settlement awarded to (against) the entity in respect of litigation.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount of increase (decrease) in loss contingency liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

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