INVENTORIES - Components of Inventories (Details) - USD ($) $ in Thousands	Sep. 26, 2020	Dec. 28, 2019
Inventory [Line Items]
Aggregate stockpiles	$ 143,271	$ 140,461
Finished goods	31,657	33,023
Work in process	10,062	7,664
Raw materials	24,784	23,639
Total	209,774	204,787
Summit Materials, LLC
Inventory [Line Items]
Aggregate stockpiles	143,271	140,461
Finished goods	31,657	33,023
Work in process	10,062	7,664
Raw materials	24,784	23,639
Total	$ 209,774	$ 204,787

Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date of merchandise or goods held by the company that are readily available for sale.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

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Amount before last-in first-out (LIFO) and valuation reserves of ore stockpile material contained on a leach pad, for example, but not limited to, copper or gold ore.

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Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date of unprocessed items to be consumed in the manufacturing or production process.

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Carrying amount, net of reserves and adjustments, as of the balance sheet date of merchandise or goods which are partially completed. This inventory is generally comprised of raw materials, labor and factory overhead costs, which require further materials, labor and overhead to be converted into finished goods, and which generally require the use of estimates to determine percentage complete and pricing.

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