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Accrued Mining and Landfill Reclamation - Narrative (Detail) - USD ($)
$ in Millions
Dec. 28, 2019
Dec. 29, 2018
Asset Retirement Obligations [Line Items]    
Anticipated costs $ 97.4 $ 92.5
Accrued expenses    
Asset Retirement Obligations [Line Items]    
Asset retirement obligation, current 7.9 4.1
Summit Materials, LLC    
Asset Retirement Obligations [Line Items]    
Anticipated costs 97.4 92.5
Summit Materials, LLC | Accrued expenses    
Asset Retirement Obligations [Line Items]    
Asset retirement obligation, current $ 7.9 $ 4.1