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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The number of limited partner units outstanding.

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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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No definition available.

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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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Number of share options (or share units) exercised during the current period.

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STOCKHOLDERS' EQUITY/MEMBERS' INTEREST - Equity Offerings (Details) - shares	3 Months Ended
	Mar. 28, 2020	Mar. 30, 2019	Dec. 28, 2019	Dec. 29, 2018
Class A Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	113,309,385	111,658,927
Exchanges during period (in shares)	196,542	17,500
Stock option exercises (in shares)	13,335
Other equity transactions (in shares)	591,335	391,104
Ending balance (in shares)	114,110,597	112,067,531
Summit Materials, Inc. and Summit Holdings, LP
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	116,559,042	115,094,445
Exchanges during period (in shares)	0	0
Stock option exercises (in shares)	13,335
Other equity transactions (in shares)	591,335	391,104
Ending balance (in shares)	117,163,712	115,485,549
LP Units \| Summit Holdings LP
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Number of LP Units outstanding, beginning balance (in shares)	3,249,657	3,435,518
Number of LP Units exchanged (in shares)	(196,542)	(17,500)
Number of LP Units outstanding, ending balance (in shares)	3,053,115	3,418,018
Summit Holdings LP
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Noncontrolling interest elimination (as a percent)	2.60%		2.80%
Summit Materials Inc
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Ownership percentage	97.40%	97.00%	97.20%	97.00%