INCOME TAXES - Narrative (Details) - USD ($)	3 Months Ended			9 Months Ended
	Oct. 02, 2021	Sep. 26, 2020	Mar. 28, 2020	Oct. 02, 2021	Sep. 26, 2020	Jan. 02, 2021
Income Taxes [Line Items]
Income tax expense (benefit)	$ 20,513,000	$ (19,613,000)		$ 33,478,000	$ (25,333,000)
Unrecognized tax benefits, decrease due to CARES Act		(32,900,000)	$ 9,500,000
Valuation allowance	1,675,000			1,675,000		$ 1,675,000
Income tax provision, interest or penalties recognized	0	0		0	0
Deferred tax asset, Investment in limited partnership	10,800,000			10,800,000
Tax receivable agreement liability	330,871,000			330,871,000		321,680,000
Tax Receivable Agreement
Income Taxes [Line Items]
Tax receivable agreement liability	330,900,000			330,900,000		$ 321,700,000
Summit Holdings LP
Income Taxes [Line Items]
Distributions to LP Unitholders				$ 0	0
Summit Holdings LP | Tax Receivable Agreement
Income Taxes [Line Items]
Percentage of benefits to be paid on tax receivable agreement				85.00%
Summit Materials, LLC
Income Taxes [Line Items]
Income tax expense (benefit)	7,016,000	(5,106,000)		$ 12,531,000	(4,877,000)
Income tax provision, interest or penalties recognized	$ 0	$ 0		$ 0	$ 0
Common Class A
Income Taxes [Line Items]
Exchanges during period (in shares)				1,440,983	196,542