The number of limited partner units exchanged.

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Represents other stockholder equity activity, in shares.

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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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The number of limited partner units outstanding.

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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 - Change in Ownership (Details) - shares	9 Months Ended	12 Months Ended
	Oct. 01, 2022	Dec. 31, 2022	Jan. 01, 2022	Jan. 02, 2021
Increase (Decrease) In Stockholders' Equity [Rollforward]
Stock option exercises (in shares)			1,745,940
Summit Materials Incorporated And Summit Holdings LP
Increase (Decrease) In Stockholders' Equity [Rollforward]
Beginning balance stockholders' equity (in shares)	121,998,328	121,998,328	119,242,979
Exchanges during period (in shares)		0	0
Stock option exercises (in shares)		10,691
Repurchases of common stock (in shares)		(3,427,510)
Other equity transactions (in shares)		1,139,150	1,009,409
Ending balance stockholders' equity (in shares)		119,720,659	121,998,328	119,242,979
LP Units \| Summit Holdings LP
Increase (Decrease) In Stockholders' Equity [Rollforward]
Number of LP Units outstanding (in shares)	1,314,006	1,314,006	2,873,170
Number of LP Units exchanged		(2,002)	(1,559,164)
Number of LP Units outstanding (in shares)		1,312,004	1,314,006	2,873,170
Common Class A
Increase (Decrease) In Stockholders' Equity [Rollforward]
Beginning balance stockholders' equity (in shares)	118,705,108	118,705,108	116,369,809	116,369,809
Exchanges during period (in shares)		2,002	1,559,164
Stock option exercises (in shares)		10,691	1,745,940
Repurchases of common stock (in shares)	(3,400,000)	(3,427,510)
Other equity transactions (in shares)		1,139,150	1,009,409
Ending balance stockholders' equity (in shares)		118,408,655	118,705,108	116,369,809
Common Class A, Including Retroactive Presentation Adjustment
Increase (Decrease) In Stockholders' Equity [Rollforward]
Beginning balance stockholders' equity (in shares)	120,684,322	120,684,322
Ending balance stockholders' equity (in shares)			120,684,322
Summit Materials Inc
Increase (Decrease) In Stockholders' Equity [Rollforward]
Summit Inc. Ownership Percentage		98.90%	98.90%	97.60%