Income Taxes - Deferred Tax Assets and Tax Receivable Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2018	Dec. 31, 2018	Dec. 30, 2017	Dec. 31, 2016	Jan. 02, 2016
Income Taxes
Income tax expense (benefit)			$ (283,977)	$ (5,299)	$ (18,263)
U.S. statutory rate			35.00%
Reduction of net deferred tax assets due to change in statutory rate	$ 216,900
Deferred tax assets subject to TRA			$ 390,000
Deferred tax assets subject to TRA, net			$ 317,000
Percentage of benefits to be paid on tax receivable agreement			85.00%
Tax receivable agreement liability			$ 331,340	58,145
Tax receivable agreement expense			271,016	14,938
Deferred tax asset, Investment in limited partnership			12,400	422,500	216,300
Alternative minimum tax credit			200
Deferred tax liability, fixed assets			147,943	184,794
Valuation Allowance
Valuation allowance			(1,675)	(502,839)	(263,825)
Exchange of L.P. Units			(31,790)	(252,456)
Release of valuation allowance and other			531,952	13,448
Other			$ 1,002	(6)
Forecast
Income Taxes
U.S. statutory rate		21.00%
Tax Receivable Agreement
Income Taxes
Percentage of benefits to be paid on tax receivable agreement			85.00%
Reclassification amount				58,100
Tax benefit deemed probable			$ 501,800
Tax Receivable Agreement | Other noncurrent liabilities
Income Taxes
Tax receivable agreement liability			331,900	59,300
Tax Receivable Agreement | Accrued expenses.
Income Taxes
Tax receivable agreement liability			600	1,100
Federal
Income Taxes
Net operating loss carryforwards			374,500
Summit Materials, LLC
Income Taxes
Income tax expense (benefit)			$ (20,345)	(5,282)	$ (18,263)
U.S. statutory rate			35.00%
Net operating loss carryforwards			$ 79,600
Alternative minimum tax credit			200
Deferred tax liability, fixed assets			47,920	58,094
Operating loss carryforwards valuation allowance recorded			1,700	2,700
Distributions to LP Unitholders			49,200	39,700
Distributions to Summit Inc.			47,500	26,700
Valuation Allowance
Valuation allowance			(1,675)	(2,677)
Summit Materials, LLC | Federal
Valuation Allowance
Loss carryforwards			(84,600)
Summit Materials, LLC | State and Local Jurisdiction
Valuation Allowance
Loss carryforwards			(63,700)
Summit Holdings LP
Income Taxes
Distributions to LP Unitholders			$ 1,700	$ 13,000