Stockholders' Equity/Members' Interest - Narrative (Details) $ / shares in Units, $ in Thousands						12 Months Ended
	Jan. 10, 2017 USD ($) $ / shares shares	Aug. 11, 2015 USD ($) $ / shares shares	Jul. 17, 2015 USD ($) shares	Mar. 17, 2015 USD ($) installment shares	Mar. 11, 2015 USD ($) $ / shares shares	Dec. 29, 2018 USD ($) shares	Dec. 30, 2017 USD ($) shares	Dec. 31, 2016 USD ($)	Nov. 30, 2015 USD ($)	Aug. 31, 2015 USD ($)	Apr. 30, 2015 USD ($)	Mar. 16, 2015 shares	May 31, 2010 shares
Subsidiary, Sale of Stock [Line Items]
Proceeds from sale of common stock, net of underwriting discounts						$ 0	$ 237,600	$ 0
Common stock issued (in shares) | shares							10,000,000
Purchase of non-controlling interest						0	$ 532	0
Continental Cement
Subsidiary, Sale of Stock [Line Items]
Aggregate consideration for acquiring noncontrolling interests				$ 64,100
Purchase of non-controlling interest				35,000
Consideration, principal amount of note issued				$ 15,000
Economic interest of redeemable non-controlling interest												70.00%
10 1/2% Senior Notes, due 2020
Subsidiary, Sale of Stock [Line Items]
Senior notes, aggregate principal amount redeemed					$ 288,200				$ 153,800	$ 183,000	$ 288,200
Noninterest Bearing Notes Payable | Continental Cement
Subsidiary, Sale of Stock [Line Items]
Number of annual installments | installment				6
Annual installments amount of non-interest bearing notes payable				$ 2,500
Summit Materials, LLC
Subsidiary, Sale of Stock [Line Items]
Purchase of non-controlling interest						$ 0	$ 532	$ 0
Summit Materials, LLC | 10 1/2% Senior Notes, due 2020
Subsidiary, Sale of Stock [Line Items]
Senior notes, aggregate principal amount redeemed									$ 153,800	$ 183,000	$ 288,200
IPO
Subsidiary, Sale of Stock [Line Items]
Proceeds from sale of common stock, net of underwriting discounts					433,000
IPO | Affiliates of the Sponsors Blackstone Management Partners and Silverhawk Summit | Termination fee paid to related parties
Subsidiary, Sale of Stock [Line Items]
Related party expense					13,800
IPO | 10 1/2% Senior Notes, due 2020
Subsidiary, Sale of Stock [Line Items]
Redemption premium					38,200
Accrued and unpaid interest					$ 5,200
IPO | Continental Cement
Subsidiary, Sale of Stock [Line Items]
Class B units purchased (in shares) | shares					71,428,571
Follow on Public Offering | Summit Holdings LP
Subsidiary, Sale of Stock [Line Items]
Number of Summit LP units purchased by Company, newly issued units (in shares) | shares		3,800,000	3,750,000
Number of Summit LP units purchased by Company from previous owners | shares		18,675,000
Follow on Public Offering | Davenport Assets
Subsidiary, Sale of Stock [Line Items]
Cash paid for acquisitions			$ 80,000
Common Class A
Subsidiary, Sale of Stock [Line Items]
Common stock issued (in shares) | shares						254,102	10,000,000
Common Class A | Continental Cement
Subsidiary, Sale of Stock [Line Items]
Consideration shares issued | shares				1,029,183
Number of class units issued (in shares) | shares												100
Common Class A | IPO
Subsidiary, Sale of Stock [Line Items]
Common stock issued (in shares) | shares					25,555,555
Offering price (in dollars per share) | $ / shares					$ 18
Common Class A | Follow on Public Offering
Subsidiary, Sale of Stock [Line Items]
Proceeds from sale of common stock, net of underwriting discounts	$ 237,600	$ 555,800
Common stock issued (in shares) | shares	10,000,000	22,425,000
Offering price (in dollars per share) | $ / shares	$ 24.05	$ 25.75
Common Class B | Continental Cement
Subsidiary, Sale of Stock [Line Items]
Number of class units issued (in shares) | shares													100,000,000
Economic interest of redeemable non-controlling interest													30.00%