Summary of Organization and Significant Accounting Policies - New Accounting Standards (Details) - USD ($) $ in Thousands	Jan. 02, 2021	Dec. 28, 2019	Dec. 30, 2018
New Accounting Standards
Operating lease right-of-use assets	$ 28,543	$ 32,777
Operating lease liability	29,688	33,808
Accounting Standards Update 2016-02
New Accounting Standards
Operating lease right-of-use assets			$ 36,800
Operating lease liability			36,800
Summit Materials, LLC
New Accounting Standards
Operating lease right-of-use assets	28,543	32,777
Operating lease liability	$ 29,688	$ 33,808
Summit Materials, LLC | Accounting Standards Update 2016-02
New Accounting Standards
Operating lease right-of-use assets			36,800
Operating lease liability			$ 36,800