Unaudited Consolidated Statements of Changes in Stockholders' Equity / Members' Interest and Redeemable Noncontrolling Interest - USD ($) $ in Thousands	Total	Summit Materials, LLC	Class A Common Stock	Class B Common Stock	Members' equity Summit Materials, LLC	Accumulated Earnings (Deficit)	Accumulated Earnings (Deficit) Summit Materials, LLC	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Summit Materials, LLC	Common Stock Class A Common Stock	Common Stock Class B Common Stock	Additional Paid-in Capital	Noncontrolling Interest in Summit Holdings
Beginning balance (in shares) at Dec. 31, 2016			97,554,278
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 81,267	$ 81,606										$ 1,154,220
LP Unit exchanges (in shares)			1,255,266
Other comprehensive loss, net of tax	9,295	9,295
Other (in shares)			1,177,200
Ending balance (in shares) at Sep. 30, 2017			109,986,744
Beginning balance at Dec. 30, 2017	1,271,721					$ 95,833		$ 7,386		$ 1,104			$ 13,178
Beginning balance at Dec. 30, 2017		1,291,594			$ 1,359,760		$ (51,031)		$ (17,135)
Beginning balance (in shares) at Dec. 30, 2017			110,350,594	100						110,350,594	100
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net contributed capital		15,615			15,615
Net income	54,957	68,433				53,069	68,433				$ 0		1,888
LP Unit exchanges (in shares)										254,102
LP Unit exchanges	0									$ 2		929	(931)
Other comprehensive loss, net of tax	(1,308)	(1,736)						(1,252)	(1,736)				(56)
Stock option exercises (in shares)										863,898
Stock option exercises	15,616									$ 9		15,607
Share-based compensation	19,833	19,833			19,833							19,833
Distributions from partnership	(69)												(69)
Distributions		(2,569)			(2,569)
Other (in shares)			1,049,856							185,958	(1)
Other	(1,880)	(1,913)			(1,913)					$ 2		(1,882)
Ending balance at Sep. 29, 2018	$ 1,358,870					$ 148,902		$ 6,134		$ 1,117	$ 0	$ 1,188,707	$ 14,010
Ending balance at Sep. 29, 2018		$ 1,389,257			$ 1,390,726		$ 17,402		$ (18,871)
Ending balance (in shares) at Sep. 29, 2018			111,654,552	99						111,654,552	99