Stockholders' Equity/Members' Interest - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 28, 2019	Dec. 29, 2018
Changes in each component of accumulated other comprehensive loss
Beginning balance stockholders' equity	$ 1,342,145	$ 1,271,721
Postretirement liability adjustment, net of tax	(1,402)	1,209
Foreign currency translation adjustment, net of tax	3,424	(6,784)
Income on cash flow hedges, net of tax		870
Income on cash flow hedges, net of tax	(1,255)
Ending balance stockholders' equity	1,444,773	1,342,145
Change in retirement plans
Changes in each component of accumulated other comprehensive loss
Beginning balance stockholders' equity	3,573	2,364
Postretirement liability adjustment, net of tax	(1,402)	1,209
Ending balance stockholders' equity	2,171	3,573
Foreign currency translation adjustment
Changes in each component of accumulated other comprehensive loss
Beginning balance stockholders' equity	(2,147)	4,637
Foreign currency translation adjustment, net of tax	3,424	(6,784)
Ending balance stockholders' equity	1,277	(2,147)
Cash flow hedge adjustments
Changes in each component of accumulated other comprehensive loss
Beginning balance stockholders' equity	1,255	385
Income on cash flow hedges, net of tax		870
Ending balance stockholders' equity		1,255
Cash flow hedge adjustments
Changes in each component of accumulated other comprehensive loss
Income on cash flow hedges, net of tax	(1,255)
Ending balance stockholders' equity	0
Accumulated Other Comprehensive Income (Loss)
Changes in each component of accumulated other comprehensive loss
Beginning balance stockholders' equity	2,681	7,386
Ending balance stockholders' equity	3,448	2,681
Summit Materials, LLC
Changes in each component of accumulated other comprehensive loss
Postretirement liability adjustment, net of tax	(1,925)	1,661
Foreign currency translation adjustment, net of tax	4,716	(9,348)
Income on cash flow hedges, net of tax		1,206
Income on cash flow hedges, net of tax	(146)
Summit Materials, LLC \| Change in retirement plans
Changes in each component of accumulated other comprehensive loss
Beginning balance stockholders' equity	(4,392)	(6,053)
Postretirement liability adjustment, net of tax	(1,925)	1,661
Ending balance stockholders' equity	(6,317)	(4,392)
Summit Materials, LLC \| Foreign currency translation adjustment
Changes in each component of accumulated other comprehensive loss
Beginning balance stockholders' equity	(19,370)	(10,022)
Foreign currency translation adjustment, net of tax	4,716	(9,348)
Ending balance stockholders' equity	(14,654)	(19,370)
Summit Materials, LLC \| Cash flow hedge adjustments
Changes in each component of accumulated other comprehensive loss
Beginning balance stockholders' equity	146	(1,060)
Income on cash flow hedges, net of tax		1,206
Ending balance stockholders' equity		146
Summit Materials, LLC \| Cash flow hedge adjustments
Changes in each component of accumulated other comprehensive loss
Income on cash flow hedges, net of tax	(146)
Ending balance stockholders' equity	0
Summit Materials, LLC \| Accumulated Other Comprehensive Income (Loss)
Changes in each component of accumulated other comprehensive loss
Beginning balance stockholders' equity	(23,616)	(17,135)
Ending balance stockholders' equity	$ (20,971)	$ (23,616)

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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Amount after tax and reclassification adjustments, of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss), attributable to parent entity.

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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, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

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