Property, Plant and Equipment, net and Intangibles, net - Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
Jan. 02, 2021	Dec. 28, 2019	Dec. 29, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 59,716	$ 33,864
Accumulated Amortization	(11,864)	(10,366)
Net Carrying Amount	47,852	23,498
Amortization expense	2,700	2,100	$ 1,500
Estimated amortization expense
2021	3,129
2022	3,136
2023	3,003
2024	2,908
2025	2,863
Thereafter	32,813
Total	47,852	23,498
Summit Materials, LLC
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	59,716	33,864
Accumulated Amortization	(11,864)	(10,366)
Net Carrying Amount	47,852	23,498
Amortization expense	2,700	2,100	$ 1,500
Estimated amortization expense
2021	3,129
2022	3,136
2023	3,003
2024	2,908
2025	2,863
Thereafter	32,813
Total	47,852	23,498
Operating permits
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	33,671	6,609
Accumulated Amortization	(1,207)	(290)
Net Carrying Amount	32,464	6,319
Mineral leases
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	19,225	19,064
Accumulated Amortization	(7,571)	(6,408)
Net Carrying Amount	11,654	12,656
Mineral leases \| Summit Materials, LLC
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	19,225	19,064
Accumulated Amortization	(7,571)	(6,408)
Net Carrying Amount	11,654	12,656
Reserve rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	6,234	6,234
Accumulated Amortization	(2,504)	(2,248)
Net Carrying Amount	3,730	3,986
Reserve rights \| Summit Materials, LLC
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	6,234	6,234
Accumulated Amortization	(2,504)	(2,248)
Net Carrying Amount	3,730	3,986
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0	1,000
Accumulated Amortization	0	(958)
Net Carrying Amount	0	42
Trade names \| Summit Materials, LLC
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0	1,000
Accumulated Amortization	0	(958)
Net Carrying Amount	0	42
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	586	957
Accumulated Amortization	(582)	(462)
Net Carrying Amount	4	495
Other \| Summit Materials, LLC
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	586	957
Accumulated Amortization	(582)	(462)
Net Carrying Amount	$ 4	$ 495

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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