Guarantor and Non-Guarantor Financial Information - Schedule of Condensed Consolidating Statements of Operations and Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Condensed Consolidating Statements of Operations
Revenue	$ 694,661	$ 634,181	$ 1,609,972	$ 1,442,551
Cost of revenue (excluding items shown separately below)	471,803	409,545	1,130,596	963,021
Depreciation, depletion, amortization and accretion	53,974	48,969	150,663	133,756
Operating income	108,167	113,911	133,921	163,571
Gain on sale of business	(12,108)	0	(12,108)	0
Income (loss) from operations before taxes	94,757	(414,046)	71,206	(415,809)
Income tax expense (benefit)	20,765	(498,333)	16,249	(497,076)
Net income	73,992	84,287	54,957	81,267
Net income attributable to Summit Inc.	71,289	81,264	53,069	78,820
Comprehensive income (loss) income attributable to member of Summit Materials, LLC	70,037	85,679	51,817	87,757
Summit Materials, LLC
Condensed Consolidating Statements of Operations
Revenue	694,661	634,181	1,609,972	1,442,551
Cost of revenue (excluding items shown separately below)	471,803	409,545	1,130,596	963,021
General and administrative expenses	60,717	61,756	194,792	182,203
Depreciation, depletion, amortization and accretion	53,974	48,969	150,663	133,756
Operating income	108,167	113,911	133,921	163,571
Other (income) expense, net	(3,371)	(2,716)	(11,793)	(3,773)
Interest expense (income)	28,720	28,708	86,066	79,195
Gain on sale of business	(12,108)	0	(12,108)	0
Income (loss) from operations before taxes	94,926	87,919	71,756	88,149
Income tax expense (benefit)	4,499	5,286	3,323	6,543
Net income	90,427	82,633	68,433	81,606
Net income (loss) attributable to noncontrolling interest	0	59	0	(27)
Net income attributable to Summit Inc.	90,427	82,574	68,433	81,633
Comprehensive income (loss) income attributable to member of Summit Materials, LLC	92,484	87,160	66,697	90,928
Summit Materials, LLC | Eliminations
Condensed Consolidating Statements of Operations
Revenue	(1,548)	(1,473)	(4,585)	(4,635)
Cost of revenue (excluding items shown separately below)	(1,548)	(1,473)	(4,585)	(4,635)
General and administrative expenses	0	0	0	0
Depreciation, depletion, amortization and accretion	0	0	0	0
Operating income	0	0	0	0
Other (income) expense, net	132,266	125,484	203,534	203,165
Interest expense (income)	0	0	0	0
Gain on sale of business	0		0
Income (loss) from operations before taxes	(132,266)	(125,484)	(203,534)	(203,165)
Income tax expense (benefit)	0	0	0	0
Net income		(125,484)		(203,165)
Net income (loss) attributable to noncontrolling interest		59		(27)
Net income attributable to Summit Inc.	(132,266)	(125,543)	(203,534)	(203,138)
Comprehensive income (loss) income attributable to member of Summit Materials, LLC	(130,209)	(120,957)	(205,270)	(193,843)
Issuers | Summit Materials, LLC | Reportable Legal Entities
Condensed Consolidating Statements of Operations
Revenue	0	0	0	0
Cost of revenue (excluding items shown separately below)	0	0	0	0
General and administrative expenses	10,951	15,011	45,175	44,718
Depreciation, depletion, amortization and accretion	574	619	1,919	1,940
Operating income	(11,525)	(15,630)	(47,094)	(46,658)
Other (income) expense, net	(132,382)	(126,386)	(204,677)	(204,877)
Interest expense (income)	29,396	28,182	87,924	76,586
Gain on sale of business	0		0
Income (loss) from operations before taxes	91,461	82,574	69,659	81,633
Income tax expense (benefit)	1,034	0	1,226	0
Net income		82,574		81,633
Net income (loss) attributable to noncontrolling interest		0		0
Net income attributable to Summit Inc.	90,427	82,574	68,433	81,633
Comprehensive income (loss) income attributable to member of Summit Materials, LLC	92,484	87,160	66,697	90,928
100% Owned Guarantors | Summit Materials, LLC | Reportable Legal Entities
Condensed Consolidating Statements of Operations
Revenue	668,145	606,046	1,548,960	1,384,956
Cost of revenue (excluding items shown separately below)	452,394	389,716	1,087,150	922,024
General and administrative expenses	46,910	44,373	141,372	131,770
Depreciation, depletion, amortization and accretion	52,213	47,032	145,135	128,851
Operating income	116,628	124,925	175,303	202,311
Other (income) expense, net	(3,019)	(1,569)	(10,563)	(1,561)
Interest expense (income)	(1,882)	(670)	(5,447)	(533)
Gain on sale of business	(12,108)		(12,108)
Income (loss) from operations before taxes	133,637	127,164	203,421	204,405
Income tax expense (benefit)	2,898	4,397	1,481	5,119
Net income		122,767		199,286
Net income (loss) attributable to noncontrolling interest		0		0
Net income attributable to Summit Inc.	130,739	122,767	201,940	199,286
Comprehensive income (loss) income attributable to member of Summit Materials, LLC	130,652	122,555	200,497	198,489
Non-Guarantors | Summit Materials, LLC | Reportable Legal Entities
Condensed Consolidating Statements of Operations
Revenue	28,064	29,608	65,597	62,230
Cost of revenue (excluding items shown separately below)	20,957	21,302	48,031	45,632
General and administrative expenses	2,856	2,372	8,245	5,715
Depreciation, depletion, amortization and accretion	1,187	1,318	3,609	2,965
Operating income	3,064	4,616	5,712	7,918
Other (income) expense, net	(236)	(245)	(87)	(500)
Interest expense (income)	1,206	1,196	3,589	3,142
Gain on sale of business	0		0
Income (loss) from operations before taxes	2,094	3,665	2,210	5,276
Income tax expense (benefit)	567	889	616	1,424
Net income		2,776		3,852
Net income (loss) attributable to noncontrolling interest		0		0
Net income attributable to Summit Inc.	1,527	2,776	1,594	3,852
Comprehensive income (loss) income attributable to member of Summit Materials, LLC	$ (443)	$ (1,598)	$ 4,773	$ (4,646)