Consolidated Statements of Changes in Stockholders' Equity / Member's Interest and Redeemable Noncontrolling Interest - USD ($) $ in Thousands	Total	Common Class A	Common Class B	Noncontrolling Interest in subsidiaries	Accumulated Earnings/Deficit	Accumulated Other Comprehensive Income (Loss)	Common Stock Common Class A	Common Stock Common Class B	Additional Paid-in Capital	Noncontrolling Interest	Summit Materials, LLC	Summit Materials, LLC Members' equity	Summit Materials, LLC Accumulated Earnings/Deficit	Summit Materials, LLC Accumulated Other Comprehensive Income (Loss)	Summit Materials, LLC Noncontrolling Interest
Beginning balance stockholders' equity at Dec. 31, 2016	$ 860,039			$ 1,378	$ 19,028	$ (2,249)	$ 961	$ 0	$ 824,304	$ 16,617
Beginning balance stockholders' equity (in shares) at Dec. 31, 2016							96,033,222	100
Beginning balance members' interest at Dec. 31, 2016											$ 876,393	$ 1,087,558	$ (185,099)	$ (27,444)	$ 1,378
Increase (Decrease) In Stockholders' Equity [Rollforward]
Net contributed capital											303,914	303,914
Net (loss) income	125,777			(27)	121,830					3,974	134,041		134,068		(27)
Issuance of shares (in shares)							10,000,000
Issuance of shares	236,971						$ 100		238,367	(1,496)
LP Unit exchanges (in shares)							1,461,677
LP Unit exchanges	0						$ 15		4,159	(4,174)
Other comprehensive income (loss), net of tax	10,021					9,635				386	10,309			10,309
Distributions											(51,986)	(51,986)
Stock option exercises (in shares)							1,203,121
Stock option exercises	21,661						$ 12		21,649
Share-based compensation	21,140								21,140		21,140	21,140
Dividend	(2)				(45,025)		$ 15		45,163	(155)
Dividend (in shares)							1,521,056
Distributions from partnership	(1,974)									(1,974)
Purchase of noncontrolling interest	(1,148)			$ (1,148)							(1,148)				(1,148)
Shares redeemed to settle taxes and other (in shares)				(203,000)			131,518
Shares redeemed to settle taxes and other	(764)						$ 1		(562)		(1,069)	(866)			(203)
Ending balance stockholders' equity at Dec. 30, 2017	1,271,721			$ 0	95,833	7,386	$ 1,104	$ 0	1,154,220	13,178				(17,135)
Ending balance stockholders' equity (in shares) at Dec. 30, 2017		110,350,594					110,350,594	100
Ending balance members' interest at Dec. 30, 2017											1,291,594	1,359,760	(51,031)	(17,135)	0
Increase (Decrease) In Stockholders' Equity [Rollforward]
Net contributed capital											15,615	15,615
Net (loss) income	36,330			0	33,906					2,424	63,837		63,837
LP Unit exchanges (in shares)		254,102					254,102
LP Unit exchanges	0						$ 2		929	(931)
Other comprehensive income (loss), net of tax	$ (4,903)					(4,705)				(198)	(6,481)			(6,481)
Distributions											(2,569)	(2,569)
Stock option exercises (in shares)	863,898	863,898					863,898
Stock option exercises	$ 15,616						$ 9		15,607
Share-based compensation	25,378								25,378		25,378	25,378
Distributions from partnership	(69)									(69)
Shares redeemed to settle taxes and other (in shares)		190,333					190,333	(1)
Shares redeemed to settle taxes and other	(1,928)						$ 2		(1,930)		(1,943)	(1,943)
Ending balance stockholders' equity at Dec. 29, 2018	1,342,145			0	129,739	2,681	$ 1,117	$ 0	1,194,204	14,404				(23,616)
Ending balance stockholders' equity (in shares) at Dec. 29, 2018		111,658,927	99				111,658,927	99
Ending balance members' interest at Dec. 29, 2018											1,385,431	1,396,241	12,806	(23,616)	0
Increase (Decrease) In Stockholders' Equity [Rollforward]
Net contributed capital											19,076	19,076
Net (loss) income	61,123				59,066					2,057	88,597		88,597
LP Unit exchanges (in shares)		185,861					185,861
LP Unit exchanges	0						$ 2		971	(973)
Other comprehensive income (loss), net of tax	$ 2,645					767				1,878	2,645			2,645
Distributions											(2,500)	(2,500)
Stock option exercises (in shares)	1,065,446	1,065,446					1,065,446
Stock option exercises	$ 19,076						$ 11		19,065
Share-based compensation	20,403								20,403		20,403	20,403
Shares redeemed to settle taxes and other (in shares)		399,151					399,151
Shares redeemed to settle taxes and other	(619)						$ 4		(623)		(502)	(502)
Ending balance stockholders' equity at Dec. 28, 2019	$ 1,444,773			$ 0	$ 188,805	$ 3,448	$ 1,134	$ 0	$ 1,234,020	$ 17,366				(20,971)
Ending balance stockholders' equity (in shares) at Dec. 28, 2019		113,309,385	99				113,309,385	99
Ending balance members' interest at Dec. 28, 2019											$ 1,513,150	$ 1,432,718	$ 101,403	$ (20,971)	$ 0