Employee Benefit Plans - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Jan. 02, 2016
Defined Benefit Plan Disclosure [Line Items]
Expense for defined contribution plans	$ 9.3	$ 8.6	$ 7.1
Actuarial loss (credit) expected to be amortized from AOCI	0.3
Summit Materials, LLC
Defined Benefit Plan Disclosure [Line Items]
Expense for defined contribution plans	$ 9.3	$ 8.6	$ 7.1