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 in Summit Inc.	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 in Summit Inc.
Beginning balance stockholders' equity at Jan. 02, 2016	$ 767,860			$ 1,362	$ 10,870	$ (2,795)	$ 497	$ 690	$ 619,003	$ 138,233
Beginning balance stockholders' equity (in shares) at Jan. 02, 2016							49,745,944	69,007,297
Beginning balance members' interest at Jan. 02, 2016											$ 778,292	$ 1,050,882	$ (245,486)	$ (28,466)	$ 1,362
Increase (Decrease) In Stockholders' Equity [Rollforward]
Net contributed capital											27,260	27,260
Net income (loss)	46,126			16	36,783					9,327	62,087		62,071		16
LP Unit exchanges (in shares)							45,124,528
LP Unit exchanges	0						$ 451		117,813	(118,264)
Other comprehensive income (loss), net of tax	1,022					546				476	1,022			1,022
Distributions											(42,192)	(42,192)
Stock option exercises (in shares)							24,354
Stock option exercises	440						$ 2		438
Class B share cancellation (in shares)								(69,007,197)
Class B share cancellation	0							$ (690)	690
Share-based compensation	49,940				(1,684)				51,624		49,940	51,624	(1,684)
Dividend (in shares)							1,135,692
Dividend	(4)				(26,941)		$ 11		27,047	(121)
Distributions from partnership	(13,034)									(13,034)
Shares redeemed to settle taxes and other (in shares)							2,704
Shares redeemed to settle taxes and other	7,689								7,689		(16)	(16)
Ending balance stockholders' equity at Dec. 31, 2016	$ 860,039			1,378	19,028	(2,249)	$ 961	$ 0	824,304	16,617
Ending balance stockholders' equity (in shares) at Dec. 31, 2016	102,705,575	97,554,278					96,033,222	100
Ending 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 income (loss)	$ 125,777			(27)	121,830					3,974	134,041		134,068		(27)
Issuance of Shares (in shares)	10,000,000	10,000,000					10,000,000
Issuance of Shares	$ 236,971						$ 100		238,367	(1,496)
LP Unit exchanges (in shares)		1,461,677					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
Purchase of noncontrolling interest	(1,148)			$ (1,148)							(1,148)				(1,148)
Dividend (in shares)							1,521,056
Dividend	(2)				(45,025)		$ 15		45,163	(155)
Distributions from partnership	$ (1,974)									(1,974)
Shares redeemed to settle taxes and other (in shares)	1,334,639	1,334,639		(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
Ending balance stockholders' equity (in shares) at Dec. 30, 2017	114,040,214	110,350,594	100				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 income (loss)	$ 36,330				33,906					2,424	63,837		63,837
Issuance of Shares (in shares)		254,102
LP Unit exchanges (in shares)	1,054,231	1,054,231					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
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	(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
Ending balance stockholders' equity (in shares) at Dec. 29, 2018	115,094,445	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