The number of limited partner units exchanged.

No definition available.

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Represents other stockholder equity activity, in shares.

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No definition available.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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- Definition

The number of limited partner units outstanding.

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- Definition

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

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No definition available.

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

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The number of shares issued during the period upon the conversion of units. An example of a convertible unit is an umbrella partnership real estate investment trust unit (UPREIT unit).

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STOCKHOLDERS' EQUITY/MEMBERS' INTEREST - Equity Offerings (Details) - shares	9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Dec. 29, 2018	Dec. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other equity transactions (in shares)	509,735	1,049,856
Class A Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	111,658,927	110,350,594
Exchanges during period (in shares)	107,336	254,102
Other equity transactions (in shares)	509,735	1,049,856
Ending balance (in shares)	112,275,998	111,654,552
Summit Materials, Inc. and Summit Holdings, LP
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	115,094,445	114,040,214
Exchanges during period (in shares)	0	0
Ending balance (in shares)	115,604,180	115,090,070
LP Units
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Number of LP Units exchanged (in shares)	(107,336)	(254,102)
LP Units \| Summit Holdings LP
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Number of LP Units outstanding, beginning balance (in shares)	3,435,518	3,689,620
Number of LP Units outstanding, ending balance (in shares)	3,328,182	3,435,518
Summit Holdings LP
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Noncontrolling interest elimination (as a percent)	2.90%		2.90%
Summit Materials Inc [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Ownership percentage	97.10%	97.00%	97.00%	96.80%