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Stock-Based Compensation - Weighted Average Assumptions Used to Estimate the Fair Value of Grants (Details)
12 Months Ended
Dec. 28, 2019
Dec. 29, 2018
Dec. 30, 2017
Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate, Minimum     2.06%
Risk-free interest rate, Maximum     2.31%
Volatility (as a percent)     47.00%
Expected term     7 years
Options | Summit Materials, LLC      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate, Minimum     2.06%
Risk-free interest rate, Maximum     2.31%
Volatility (as a percent)     47.00%
Expected term     7 years
Performance Stock Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate (as a percent) 2.49% 2.38% 1.45%
Volatility (as a percent) 36.00% 38.00% 39.00%
Expected term 3 years 3 years 3 years
Performance Stock Units | Summit Materials, LLC      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate (as a percent) 2.49% 2.38% 1.45%
Volatility (as a percent) 36.00% 38.00% 39.00%
Expected term 3 years 3 years 3 years