Employee Benefit Plans - Fair Value of Company's Pension Plans' Assets (Detail) - USD ($) $ in Thousands	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	$ 17,449	$ 19,012
Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	17,449	19,012
Intermediate—government
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	3,547	3,620
Intermediate—government | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	3,547	3,620
Intermediate—corporate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	3,437	3,872
Intermediate—corporate | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	3,437	3,872
Short-term—government
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	756	497
Short-term—government | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	756	497
Short-term—corporate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	957	1,702
Short-term—corporate | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	957	1,702
International
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	1,143
International | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	1,143
U.S. Large cap value
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	978	1,765
U.S. Large cap value | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	978	1,765
U.S. Large cap growth
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	976	588
U.S. Large cap growth | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	976	588
U.S. Mid cap value
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	471	586
U.S. Mid cap value | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	471	586
U.S. Mid cap growth
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	496	586
U.S. Mid cap growth | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	496	586
U.S. Small cap value
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	463	571
U.S. Small cap value | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	463	571
U.S. Small cap growth
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	474	580
U.S. Small cap growth | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	474	580
Managed Futures
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	355	392
Managed Futures | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	355	392
International
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	1,004	1,547
International | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	1,004	1,547
Emerging Markets
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	362
Emerging Markets | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	362
Commodities Broad Basket
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	1,048	801
Commodities Broad Basket | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	1,048	801
Cash
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	982	1,522
Cash | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	982	1,522
Precious metals
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value		383
Precious metals | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value		383
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	17,449	19,012	$ 18,395
Pension Benefits | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	17,449	19,012	$ 18,395
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	10,222	9,301
Quoted Prices in Active Markets for Identical Assets (Level 1) | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	10,222	9,301
Quoted Prices in Active Markets for Identical Assets (Level 1) | Intermediate—government
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	3,547	3,068
Quoted Prices in Active Markets for Identical Assets (Level 1) | Intermediate—government | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	3,547	3,068
Quoted Prices in Active Markets for Identical Assets (Level 1) | Intermediate—corporate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Intermediate—corporate | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term—government
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	756	497
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term—government | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	756	497
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term—corporate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term—corporate | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | International
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | International | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Large cap value
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	978	1,765
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Large cap value | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	978	1,765
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Large cap growth
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	976	588
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Large cap growth | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	976	588
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Mid cap value
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	471	586
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Mid cap value | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	471	586
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Mid cap growth
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	496	586
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Mid cap growth | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	496	586
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Small cap value
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	463	571
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Small cap value | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	463	571
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Small cap growth
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	474	580
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Small cap growth | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	474	580
Quoted Prices in Active Markets for Identical Assets (Level 1) | Managed Futures
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Managed Futures | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | International
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	329	677
Quoted Prices in Active Markets for Identical Assets (Level 1) | International | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	329	677
Quoted Prices in Active Markets for Identical Assets (Level 1) | Emerging Markets
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	362
Quoted Prices in Active Markets for Identical Assets (Level 1) | Emerging Markets | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	362
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commodities Broad Basket
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	388	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commodities Broad Basket | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	388	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	982	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	982	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Precious metals
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value		383
Quoted Prices in Active Markets for Identical Assets (Level 1) | Precious metals | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value		383
Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	7,227	9,711
Observable Inputs (Level 2) | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	7,227	9,711
Observable Inputs (Level 2) | Intermediate—government
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	552
Observable Inputs (Level 2) | Intermediate—government | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	552
Observable Inputs (Level 2) | Intermediate—corporate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	3,437	3,872
Observable Inputs (Level 2) | Intermediate—corporate | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	3,437	3,872
Observable Inputs (Level 2) | Short-term—government
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Observable Inputs (Level 2) | Short-term—government | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Observable Inputs (Level 2) | Short-term—corporate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	957	1,702
Observable Inputs (Level 2) | Short-term—corporate | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	957	1,702
Observable Inputs (Level 2) | International
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	1,143
Observable Inputs (Level 2) | International | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	1,143
Observable Inputs (Level 2) | U.S. Large cap value
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Observable Inputs (Level 2) | U.S. Large cap value | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Observable Inputs (Level 2) | U.S. Large cap growth
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Observable Inputs (Level 2) | U.S. Large cap growth | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Observable Inputs (Level 2) | U.S. Mid cap value
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Observable Inputs (Level 2) | U.S. Mid cap value | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Observable Inputs (Level 2) | U.S. Mid cap growth
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Observable Inputs (Level 2) | U.S. Mid cap growth | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Observable Inputs (Level 2) | U.S. Small cap value
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Observable Inputs (Level 2) | U.S. Small cap value | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Observable Inputs (Level 2) | U.S. Small cap growth
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Observable Inputs (Level 2) | U.S. Small cap growth | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	0
Observable Inputs (Level 2) | Managed Futures
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	355	392
Observable Inputs (Level 2) | Managed Futures | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	355	392
Observable Inputs (Level 2) | International
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	675	870
Observable Inputs (Level 2) | International | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	675	870
Observable Inputs (Level 2) | Emerging Markets
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0
Observable Inputs (Level 2) | Emerging Markets | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0
Observable Inputs (Level 2) | Commodities Broad Basket
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	660	801
Observable Inputs (Level 2) | Commodities Broad Basket | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	660	801
Observable Inputs (Level 2) | Cash
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	0	1,522
Observable Inputs (Level 2) | Cash | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value	$ 0	1,522
Observable Inputs (Level 2) | Precious metals
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value		0
Observable Inputs (Level 2) | Precious metals | Summit Materials, LLC
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total fair value		$ 0