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 at Dec. 30, 2017	$ 1,271,721					$ 95,833		$ 7,386		$ 1,104	$ 0	$ 1,154,220	$ 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							110,350,594	100
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net contributed capital		15,475			15,475
Net income (loss)	(55,948)	(68,596)				(53,729)	(68,596)						(2,219)
LP Unit exchanges (in shares)										104,104
LP Unit exchanges	0									$ 1		485	(486)
Other comprehensive income, net of tax	(2,629)	(2,109)						(2,563)	(2,109)				(66)
Stock option exercises (in shares)										856,915
Stock option exercises	15,477									$ 9		15,468
Share-based compensation	8,507	8,507			8,507							8,507
Distributions from partnership	(9)												(9)
Distributions		(2,509)			(2,509)
Other (in shares)										176,960
Shares redeemed to settle taxes and other	(1,772)	(1,820)			(1,820)					$ 2		(1,774)
Ending balance at Mar. 31, 2018	1,235,347					42,104		4,823		$ 1,116	$ 0	1,176,906	10,398
Ending balance at Mar. 31, 2018		1,240,542			1,379,413		(119,627)		(19,244)
Ending balance (in shares) at Mar. 31, 2018										111,488,573	100
Beginning balance at Dec. 30, 2017	1,271,721					95,833		7,386		$ 1,104	$ 0	1,154,220	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							110,350,594	100
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(19,035)	(21,994)
LP Unit exchanges (in shares)			229,658
Other comprehensive income, net of tax	$ (2,858)	(3,793)
Other (in shares)	1,048,986		1,048,986
Ending balance at Jun. 30, 2018	$ 1,277,771					77,613		4,645		$ 1,117	$ 0	1,183,071	11,325
Ending balance at Jun. 30, 2018		1,291,139			1,385,092		(73,025)		(20,928)
Ending balance (in shares) at Jun. 30, 2018			111,629,238							111,629,238	100
Beginning balance at Mar. 31, 2018	1,235,347					42,104		4,823		$ 1,116	$ 0	1,176,906	10,398
Beginning balance at Mar. 31, 2018		1,240,542			1,379,413		(119,627)		(19,244)
Beginning balance (in shares) at Mar. 31, 2018										111,488,573	100
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net contributed capital		140			140
Net income (loss)	36,913	46,602				35,509	46,602						1,404
LP Unit exchanges (in shares)										125,554
LP Unit exchanges	0									$ 1		365	(366)
Other comprehensive income, net of tax	(229)	(1,684)						(178)	(1,684)				(51)
Stock option exercises	139											139
Share-based compensation	5,683	5,683			5,683							5,683
Distributions from partnership	(60)												(60)
Distributions		(60)			(60)
Other (in shares)										15,111
Shares redeemed to settle taxes and other	(22)	(84)			(84)							(22)
Ending balance at Jun. 30, 2018	1,277,771					77,613		4,645		$ 1,117	$ 0	1,183,071	11,325
Ending balance at Jun. 30, 2018		1,291,139			1,385,092		(73,025)		(20,928)
Ending balance (in shares) at Jun. 30, 2018			111,629,238							111,629,238	100
Beginning balance at Dec. 29, 2018	1,342,145					129,739		2,681		$ 1,117	$ 0	1,194,204	14,404
Beginning balance at Dec. 29, 2018		1,385,431			1,396,241		12,806		(23,616)
Beginning balance (in shares) at Dec. 29, 2018			111,658,927	99						111,658,927	99
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net contributed capital		766			766
Net income (loss)	(71,501)	(91,564)				(68,772)	(91,564)						(2,729)
LP Unit exchanges (in shares)										17,500
LP Unit exchanges	0											122	(122)
Other comprehensive income, net of tax	1,650	2,192						1,584	2,192				66
Stock option exercises (in shares)										43,142
Stock option exercises	767									$ 1		766
Share-based compensation	5,906	5,906			5,906							5,906
Distributions		(2,500)			(2,500)
Other (in shares)										347,962
Shares redeemed to settle taxes and other	(492)	(501)			(501)					$ 3		(495)
Ending balance at Mar. 30, 2019	1,278,475					60,967		4,265		$ 1,121	$ 0	1,200,503	11,619
Ending balance at Mar. 30, 2019		1,299,730			1,399,912		(78,758)		(21,424)
Ending balance (in shares) at Mar. 30, 2019										112,067,531	99
Beginning balance at Dec. 29, 2018	1,342,145					129,739		2,681		$ 1,117	$ 0	1,194,204	14,404
Beginning balance at Dec. 29, 2018		1,385,431			1,396,241		12,806		(23,616)
Beginning balance (in shares) at Dec. 29, 2018			111,658,927	99						111,658,927	99
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(33,511)	(38,063)
LP Unit exchanges (in shares)			17,500
Other comprehensive income, net of tax	$ 3,238	4,288
Other (in shares)	397,067		397,067
Ending balance at Jun. 29, 2019	$ 1,322,771					97,377		5,791		$ 1,122	$ 0	1,205,221	13,260
Ending balance at Jun. 29, 2019		1,360,044			1,404,629		(25,257)		(19,328)
Ending balance (in shares) at Jun. 29, 2019			112,073,494	99						112,073,494	99
Beginning balance at Mar. 30, 2019	1,278,475					60,967		4,265		$ 1,121	$ 0	1,200,503	11,619
Beginning balance at Mar. 30, 2019		1,299,730			1,399,912		(78,758)		(21,424)
Beginning balance (in shares) at Mar. 30, 2019										112,067,531	99
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net contributed capital		18			18
Net income (loss)	37,990	53,501				36,410	53,501						1,580
Other comprehensive income, net of tax	1,588	2,096						1,526	2,096				62
Stock option exercises (in shares)										1,019
Stock option exercises	17									$ 0		17
Share-based compensation	4,699	4,699			4,699							4,699
Other (in shares)										4,944
Shares redeemed to settle taxes and other	2									$ 1		2	(1)
Ending balance at Jun. 29, 2019	$ 1,322,771					$ 97,377		$ 5,791		$ 1,122	$ 0	$ 1,205,221	$ 13,260
Ending balance at Jun. 29, 2019		$ 1,360,044			$ 1,404,629		$ (25,257)		$ (19,328)
Ending balance (in shares) at Jun. 29, 2019			112,073,494	99						112,073,494	99