Consolidated Statements of Changes in Stockholders' Equity / Member's Interest and Redeemable Noncontrolling Interest - USD ($)	Summit Materials, LLC Members' equity	Summit Materials, LLC Total Member's Interest	Summit Materials, LLC Noncontrolling Interest in subsidiaries	Summit Materials, LLC Accumulated Earnings/Deficit	Summit Materials, LLC Accumulated Other Comprehensive Operations	Summit Materials, LLC	Noncontrolling Interest in subsidiaries	Accumulated Earnings/Deficit	Accumulated Other Comprehensive Operations	Common Stock Common Class A	Common Stock Common Class B	Additional Paid-in Capital	Noncontrolling Interest in Summit Inc.	Common Class A	Common Class B	Total
Beginning Balance (in shares) at Jan. 02, 2016														50,881,636
Increase (decrease) in stockholders' equity / members' interest and redeemable noncontrolling interest
Issuance of Shares (in shares)														1,038
Ending Balance (in shares) at Apr. 02, 2016														50,882,674
Beginning Balance (in shares) at Jan. 02, 2016														50,881,636
Increase (decrease) in stockholders' equity / members' interest and redeemable noncontrolling interest
Net (loss) income						$ 40,876,000										$ 40,077,000
Other comprehensive income						734,000										734,000
Ending Balance (in shares) at Oct. 01, 2016														76,702,011
Beginning Balance (in shares) at Apr. 02, 2016														50,882,674
Increase (decrease) in stockholders' equity / members' interest and redeemable noncontrolling interest
LP Unit exchanges (in shares)														13,177,754
Other (in shares)														6,250
Ending Balance (in shares) at Jul. 02, 2016														64,066,678
Increase (decrease) in stockholders' equity / members' interest and redeemable noncontrolling interest
Net (loss) income						61,360,000										61,106,000
LP Unit exchanges (in shares)														12,634,500
Other comprehensive income						(1,251,000)										(1,251,000)
Other (in shares)														833
Ending Balance (in shares) at Oct. 01, 2016														76,702,011
Beginning Balance at Dec. 31, 2016							$ 1,378,000
Beginning Balance at Dec. 31, 2016								$ 19,028,000	$ (2,249,000)	$ 961,000	$ 100	$ 824,304,000	$ 16,617,000			860,039,000
Beginning Balance at Dec. 31, 2016	$ 1,087,558,000	$ 876,393,000	$ 1,378,000	$ (185,099,000)	$ (27,444,000)	876,393,000
Beginning Balance (in shares) at Dec. 31, 2016										96,033,222				96,033,222	100
Increase (decrease) in stockholders' equity / members' interest and redeemable noncontrolling interest
Issuance of Shares (in shares)														10,000,000
LP Unit exchanges (in shares)														236,095
Other (in shares)														134,423
Ending Balance (in shares) at Apr. 01, 2017														106,403,740
Beginning Balance at Dec. 31, 2016							1,378,000
Beginning Balance at Dec. 31, 2016								19,028,000	(2,249,000)	$ 961,000	$ 100	824,304,000	16,617,000			860,039,000
Beginning Balance at Dec. 31, 2016	1,087,558,000	876,393,000	1,378,000	(185,099,000)	(27,444,000)	876,393,000
Beginning Balance (in shares) at Dec. 31, 2016										96,033,222				96,033,222	100
Increase (decrease) in stockholders' equity / members' interest and redeemable noncontrolling interest
Net contributed capital	256,040,000	256,040,000
Net (loss) income		81,606,000	(27,000)	81,633,000		81,606,000		76,608,000					2,474,000			79,055,000
Net (loss) income							(27,000)
Issuance of Shares										$ 100,000		238,367,000	(1,496,000)			236,971,000
Issuance of Shares (in shares)										10,000,000
LP Unit exchanges										$ 12,000		3,379,000	(3,391,000)
LP Unit exchanges (in shares)										1,255,266
Other comprehensive income		9,295,000			9,295,000	9,295,000			8,937,000				358,000			9,295,000
Share-based compensation	14,148,000	14,148,000										14,148,000				14,148,000
Distributions	(2,609,000)	(2,609,000)
Distributions from partnership													(109,000)			(109,000)
Other										$ 12,000		17,953,000				17,965,000
Other (in shares)										1,177,200
Other	(845,000)	(845,000)
Ending Balance at Sep. 30, 2017								95,636,000	6,688,000	$ 1,085,000		1,098,151,000	14,453,000			1,217,364,000
Ending Balance at Sep. 30, 2017	1,354,292,000	1,234,028,000	1,351,000	(103,466,000)	(18,149,000)	1,234,028,000
Ending Balance at Sep. 30, 2017							1,351,000
Ending Balance (in shares) at Sep. 30, 2017										108,465,688	100			108,465,688	100
Beginning Balance (in shares) at Apr. 01, 2017														106,403,740
Increase (decrease) in stockholders' equity / members' interest and redeemable noncontrolling interest
LP Unit exchanges (in shares)														778,064
Other (in shares)														310,175
Ending Balance (in shares) at Jul. 01, 2017														107,491,979
Increase (decrease) in stockholders' equity / members' interest and redeemable noncontrolling interest
Net (loss) income						82,633,000										82,075,000
LP Unit exchanges (in shares)														241,107
Other comprehensive income						4,586,000										4,586,000
Other (in shares)														732,602
Ending Balance at Sep. 30, 2017								$ 95,636,000	$ 6,688,000	$ 1,085,000		$ 1,098,151,000	$ 14,453,000			$ 1,217,364,000
Ending Balance at Sep. 30, 2017	$ 1,354,292,000	$ 1,234,028,000	$ 1,351,000	$ (103,466,000)	$ (18,149,000)	$ 1,234,028,000
Ending Balance at Sep. 30, 2017							$ 1,351,000
Ending Balance (in shares) at Sep. 30, 2017										108,465,688	100			108,465,688	100