STOCKHOLDERS' EQUITY/MEMBERS' INTEREST - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 28, 2019	Sep. 29, 2018
Changes in each component of accumulated other comprehensive loss
Beginning balance	$ 1,327,741
Foreign currency translation adjustment, net of tax	2,364	$ (2,295)
(Loss) income on cash flow hedges, net of tax	(107)	1,043
Ending balance	1,371,436
Summit Materials, LLC
Changes in each component of accumulated other comprehensive loss
Foreign currency translation adjustment, net of tax	3,263	(3,179)
(Loss) income on cash flow hedges, net of tax	(148)	1,443
Change in retirement plans
Changes in each component of accumulated other comprehensive loss
Beginning balance	3,573	2,364
Ending balance	3,573	2,364
Change in retirement plans \| Summit Materials, LLC
Changes in each component of accumulated other comprehensive loss
Beginning balance	(4,392)	(6,053)
Ending balance	(4,392)	(6,053)
Foreign currency translation adjustments
Changes in each component of accumulated other comprehensive loss
Beginning balance	(2,147)	4,637
Foreign currency translation adjustment, net of tax	2,364	(2,295)
Ending balance	217	2,342
Foreign currency translation adjustments \| Summit Materials, LLC
Changes in each component of accumulated other comprehensive loss
Beginning balance	(19,370)	(10,022)
Foreign currency translation adjustment, net of tax	3,263	(3,179)
Ending balance	(16,107)	(13,201)
Cash flow hedge adjustments
Changes in each component of accumulated other comprehensive loss
Beginning balance	1,255	385
(Loss) income on cash flow hedges, net of tax	(107)	1,043
Ending balance	1,148	1,428
Cash flow hedge adjustments \| Summit Materials, LLC
Changes in each component of accumulated other comprehensive loss
Beginning balance	146	(1,060)
(Loss) income on cash flow hedges, net of tax	(148)	1,443
Ending balance	(2)	383
Accumulated other comprehensive income (loss)
Changes in each component of accumulated other comprehensive loss
Beginning balance	2,681	7,386
Ending balance	4,938	6,134
Accumulated other comprehensive income (loss) \| Summit Materials, LLC
Changes in each component of accumulated other comprehensive loss
Beginning balance	(23,616)	(17,135)
Ending balance	$ (20,501)	$ (18,871)

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Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature, attributable to parent entity.

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Amount, after tax and reclassification, of gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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