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Duration of a fiscal period, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but not limited to, weeks in a year or quarter.

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The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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Number of new stock issued during the period.

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Summary of Organization and Significant Accounting Policies - General Information and Equity Offerings (Details) $ in Thousands			1 Months Ended	12 Months Ended
	Aug. 13, 2015 USD ($)	Jul. 17, 2015 USD ($)	Aug. 13, 2015 USD ($)	Dec. 30, 2017 USD ($) segment facility shares	Dec. 31, 2016 shares	Jan. 02, 2016 USD ($)	Mar. 16, 2015
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements
Number of plants \| facility				2
Number of operating segments \| segment				3
Length of fiscal quarter				91 days
Interval period for 53 week fiscal year				7 years
Equity Offering
Proceeds from sale of common stock, net of underwriting discounts				$ 237,600		$ 1,037,444
Percentage of benefits to be paid on tax receivable agreement				85.00%
Principles of Consolidation
Voting power (as a percent)				96.80%	95.00%	51.00%
Minimum
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements
Length of fiscal year				364 days
Maximum
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements
Length of fiscal year				371 days
Continental Cement
Principles of Consolidation
Ownership Percentage							70.00%
Davenport Assets
Equity Offering
Cash paid for acquisitions	$ 80,000	$ 370,000	$ 450,000
Summit Materials, LLC
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements
Number of plants \| facility				2
Number of operating segments \| segment				3
Length of fiscal quarter				91 days
Interval period for 53 week fiscal year				7 years
Summit Materials, LLC \| Minimum
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements
Length of fiscal year				364 days
Summit Materials, LLC \| Maximum
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements
Length of fiscal year				371 days
Summit Materials, LLC \| Continental Cement
Principles of Consolidation
Noncontrolling interest elimination (as a percent)				30.00%
Summit Materials, LLC \| Ohio Valley Asphalt
Principles of Consolidation
Noncontrolling interest elimination (as a percent)				20.00%
Summit Materials, LLC \| Davenport Assets
Equity Offering
Cash paid for acquisitions	$ 450,000	$ 370,000
Summit Holdings LP
Principles of Consolidation
Voting power (as a percent)				100.00%
Noncontrolling interest elimination (as a percent)				3.20%	5.00%
Summit Materials, Inc. and Summit Holdings, LP
Equity Offering
Common stock issued (in shares) \| shares				10,000,000	1,038