Employee Benefit Plans - Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost (Detail)	12 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Jan. 02, 2016
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return on plan assets, net periodic benefit cost	7.00%	7.30%	7.30%
Pension Benefits | Summit Materials, LLC
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return on plan assets, net periodic benefit cost	7.00%	7.30%	7.30%
Pension Benefits | Minimum
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.61%	3.74%	3.50%
Pension Benefits | Minimum | Summit Materials, LLC
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.61%	3.74%	3.50%
Pension Benefits | Maximum
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.81%	3.97%	3.98%
Pension Benefits | Maximum | Summit Materials, LLC
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.81%	3.97%	3.98%
Healthcare & Life Ins
Defined Benefit Plan Disclosure [Line Items]
Discount rate			3.39%
Healthcare & Life Ins | Summit Materials, LLC
Defined Benefit Plan Disclosure [Line Items]
Discount rate			3.39%
Healthcare & Life Ins | Minimum
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.54%	3.34%
Healthcare & Life Ins | Minimum | Summit Materials, LLC
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.54%	3.34%
Healthcare & Life Ins | Maximum
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.65%	3.80%	3.52%
Healthcare & Life Ins | Maximum | Summit Materials, LLC
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.65%	3.80%	3.52%