Fair Value of Financial Instruments - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 29, 2018 USD ($)
Interest rate derivatives | Term Loan, due 2022 | Cash flow hedges
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Term loan borrowings hedged by derivatives	$ 200.0
Interest rate derivatives | Term Loan, due 2022 | Cash flow hedges | Summit Materials, LLC
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Term loan borrowings hedged by derivatives	$ 200.0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	10.00%
Level 3 | Summit Materials, LLC
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	10.00%