Stockholders' Equity/Members' Interest - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
Changes in each component of accumulated other comprehensive loss
Beginning balance	$ 1,258,543
Postretirement curtailment adjustment, net of tax		$ 309
Postretirement liability adjustment, net of tax	1,209	605
Foreign currency translation adjustment, net of tax	(6,784)	7,743
Income on cash flow hedges, net of tax	870	978
Ending balance	1,327,741	1,258,543
Accumulated Other Comprehensive Operations
Changes in each component of accumulated other comprehensive loss
Beginning balance	7,386	(2,249)
Ending balance	2,681	7,386	$ (2,249)
Change in retirement plans
Changes in each component of accumulated other comprehensive loss
Beginning balance	2,364	1,450
Postretirement curtailment adjustment, net of tax		309
Postretirement liability adjustment, net of tax	1,209	605
Ending balance	3,573	2,364	1,450
Foreign currency translation adjustment
Changes in each component of accumulated other comprehensive loss
Beginning balance	4,637	(3,106)
Foreign currency translation adjustment, net of tax	(6,784)	7,743
Ending balance	(2,147)	4,637	(3,106)
Cash flow hedge adjustments
Changes in each component of accumulated other comprehensive loss
Beginning balance	385	(593)
Income on cash flow hedges, net of tax	870	978
Ending balance	1,255	385	(593)
Summit Materials, LLC
Changes in each component of accumulated other comprehensive loss
Postretirement curtailment adjustment, net of tax		429	0
Postretirement liability adjustment, net of tax	1,661	699	(688)
Foreign currency translation adjustment, net of tax	(9,348)	7,768
Income on cash flow hedges, net of tax	1,206
Summit Materials, LLC | Accumulated Other Comprehensive Operations
Changes in each component of accumulated other comprehensive loss
Beginning balance	(17,135)	(27,444)
Income on cash flow hedges, net of tax		1,413
Ending balance	(23,616)	(17,135)	(27,444)
Summit Materials, LLC | Change in retirement plans
Changes in each component of accumulated other comprehensive loss
Beginning balance	(6,053)	(7,181)
Postretirement curtailment adjustment, net of tax		429
Postretirement liability adjustment, net of tax	1,661
Ending balance	(4,392)	(6,053)	(7,181)
Summit Materials, LLC | Foreign currency translation adjustment
Changes in each component of accumulated other comprehensive loss
Beginning balance	(10,022)	(17,790)
Foreign currency translation adjustment, net of tax	(9,348)	7,768
Ending balance	(19,370)	(10,022)	(17,790)
Summit Materials, LLC | Cash flow hedge adjustments
Changes in each component of accumulated other comprehensive loss
Beginning balance	(1,060)	(2,473)
Income on cash flow hedges, net of tax	1,206	1,413
Ending balance	$ 146	$ (1,060)	$ (2,473)