SEGMENT INFORMATION - Financial Data (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 29, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 29, 2019 USD ($) segment	Jun. 30, 2018 USD ($)	Dec. 29, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment			3
Number of reportable segments | segment			3
Total revenue	$ 600,891	$ 600,890	$ 933,530	$ 915,311
Income (loss) from operation before taxes	54,697	49,103	(44,841)	(23,551)
Interest expense	29,401	28,943	59,506	57,727
Depreciation, depletion and amortization	53,035	49,402	107,842	95,945
Accretion	590	329	1,171	744
Loss on debt financings	0	149	14,565	149
Transaction costs	390	1,291	698	2,557
Non-cash compensation	4,699	5,683	10,605	14,190
Other	(2,346)	441	(2,492)	(6,907)
Total Adjusted EBITDA	140,466	135,341	147,054	140,854
Total purchases of property, plant and equipment			105,569	131,657
Total depreciation, depletion, amortization and accretion	53,625	49,731	109,013	96,689
Total assets	3,954,856		3,954,856		$ 3,857,641
West
Segment Reporting Information [Line Items]
Total revenue	300,212	321,713	482,157	503,426
East
Segment Reporting Information [Line Items]
Total revenue	216,132	197,336	329,520	292,493
Cement
Segment Reporting Information [Line Items]
Total revenue	84,547	81,841	121,853	119,392
Operating segment
Segment Reporting Information [Line Items]
Total purchases of property, plant and equipment			104,785	127,938
Total depreciation, depletion, amortization and accretion	52,633	49,096	107,069	95,344
Total assets	3,632,698		3,632,698		3,501,727
Operating segment | West
Segment Reporting Information [Line Items]
Total Adjusted EBITDA	54,820	61,227	69,118	77,400
Total purchases of property, plant and equipment			51,517	76,223
Total depreciation, depletion, amortization and accretion	22,924	22,589	46,849	44,740
Total assets	1,437,583		1,437,583		1,370,501
Operating segment | East
Segment Reporting Information [Line Items]
Total Adjusted EBITDA	54,412	45,395	57,654	42,192
Total purchases of property, plant and equipment			41,801	37,303
Total depreciation, depletion, amortization and accretion	19,840	17,826	40,051	35,553
Total assets	1,307,364		1,307,364		1,253,640
Operating segment | Cement
Segment Reporting Information [Line Items]
Total Adjusted EBITDA	35,441	34,660	32,854	38,327
Total purchases of property, plant and equipment			11,467	14,412
Total depreciation, depletion, amortization and accretion	9,869	8,681	20,169	15,051
Total assets	887,751		887,751		877,586
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Total Adjusted EBITDA	(4,207)	(5,941)	(12,572)	(17,065)
Total purchases of property, plant and equipment			784	3,719
Total depreciation, depletion, amortization and accretion	992	635	1,944	1,345
Total assets	322,158		$ 322,158		355,914
Summit Materials, LLC
Segment Reporting Information [Line Items]
Number of operating segments | segment			3
Number of reportable segments | segment			3
Total revenue	600,891	600,890	$ 933,530	915,311
Income (loss) from operation before taxes	54,815	49,270	(44,555)	(23,170)
Interest expense	29,283	28,776	59,220	57,346
Depreciation, depletion and amortization	53,035	49,402	107,842	95,945
Accretion	590	329	1,171	744
Loss on debt financings	0	149	14,565	149
Transaction costs	390	1,291	698	2,557
Non-cash compensation	4,699	5,683	10,605	14,190
Other	(2,346)	441	(2,492)	(6,907)
Total Adjusted EBITDA	140,466	135,341	147,054	140,854
Total purchases of property, plant and equipment			105,569	131,657
Total depreciation, depletion, amortization and accretion	53,625	49,731	109,013	96,689
Total assets	3,718,767		3,718,767		3,633,244
Summit Materials, LLC | West
Segment Reporting Information [Line Items]
Total revenue	300,212	321,713	482,157	503,426
Summit Materials, LLC | East
Segment Reporting Information [Line Items]
Total revenue	216,132	197,336	329,520	292,493
Summit Materials, LLC | Cement
Segment Reporting Information [Line Items]
Total revenue	84,547	81,841	121,853	119,392
Summit Materials, LLC | Operating segment
Segment Reporting Information [Line Items]
Total purchases of property, plant and equipment			104,785	127,938
Total depreciation, depletion, amortization and accretion	52,633	49,096	107,069	95,344
Total assets	3,632,698		3,632,698		3,501,727
Summit Materials, LLC | Operating segment | West
Segment Reporting Information [Line Items]
Total Adjusted EBITDA	54,820	61,227	69,118	77,400
Total purchases of property, plant and equipment			51,517	76,223
Total depreciation, depletion, amortization and accretion	22,924	22,589	46,849	44,740
Total assets	1,437,583		1,437,583		1,370,501
Summit Materials, LLC | Operating segment | East
Segment Reporting Information [Line Items]
Total Adjusted EBITDA	54,412	45,395	57,654	42,192
Total purchases of property, plant and equipment			41,801	37,303
Total depreciation, depletion, amortization and accretion	19,840	17,826	40,051	35,553
Total assets	1,307,364		1,307,364		1,253,640
Summit Materials, LLC | Operating segment | Cement
Segment Reporting Information [Line Items]
Total Adjusted EBITDA	35,441	34,660	32,854	38,327
Total purchases of property, plant and equipment			11,467	14,412
Total depreciation, depletion, amortization and accretion	9,869	8,681	20,169	15,051
Total assets	887,751		887,751		877,586
Summit Materials, LLC | Corporate, Non-Segment
Segment Reporting Information [Line Items]
Total Adjusted EBITDA	(4,207)	(5,941)	(12,572)	(17,065)
Total purchases of property, plant and equipment			784	3,719
Total depreciation, depletion, amortization and accretion	992	$ 635	1,944	$ 1,345
Total assets	$ 86,069		$ 86,069		$ 131,517