Stockholders' Equity - General Information and Equity Offerings (Details) $ / shares in Units, $ in Thousands									1 Months Ended		12 Months Ended
	Jan. 10, 2017 USD ($) $ / shares shares	Dec. 28, 2016 shares	Dec. 22, 2016 shares	Aug. 13, 2015 USD ($)	Aug. 11, 2015 USD ($) $ / shares shares	Jul. 17, 2015 USD ($) facility	Mar. 17, 2015 USD ($) item shares	Mar. 11, 2015 USD ($) $ / shares shares	Aug. 13, 2015 USD ($)	Apr. 25, 2015 USD ($)	Dec. 30, 2017 USD ($) segment facility shares	Dec. 31, 2016 shares	Jan. 02, 2016 USD ($) shares	Nov. 28, 2015 USD ($)	Aug. 22, 2015 USD ($)	Mar. 16, 2015 shares	May 31, 2010 shares
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements
Number of plants | facility											2
Number of operating segments | segment											3
Length of fiscal quarter											91 days
Interval period for 53 week fiscal year											7 years
Equity Offering
Proceeds from sale of common stock, net of underwriting discounts | $											$ 237,600		$ 1,037,444
Redeemable Noncontrolling Interest
Cash consideration | $											$ 532		$ 497,848
Voting power (as a percent)											96.80%	95.00%	51.00%
Minimum
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements
Length of fiscal year											364 days
Maximum
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements
Length of fiscal year											371 days
Continental Cement
Redeemable Noncontrolling Interest
Aggregate consideration for acquiring noncontrolling interests | $							$ 64,100
Cash consideration | $							35,000
Consideration, Principal amount of note issued | $							$ 15,000
Economic interest of redeemable noncontrolling interest, approximately																70.00%
Ownership Percentage																70.00%
Davenport Assets
Equity Offering
Cash paid for acquisitions | $				$ 80,000		$ 370,000			$ 450,000
Summit Materials, LLC
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements
Number of plants | facility											2
Number of operating segments | segment											3
Length of fiscal quarter											91 days
Interval period for 53 week fiscal year											7 years
Redeemable Noncontrolling Interest
Cash consideration | $											$ 532
Summit Materials, LLC | Minimum
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements
Length of fiscal year											364 days
Summit Materials, LLC | Maximum
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements
Length of fiscal year											371 days
Summit Materials, LLC | Continental Cement
Redeemable Noncontrolling Interest
Noncontrolling interest elimination (as a percent)											30.00%
Summit Materials, LLC | Ohio Valley Asphalt
Redeemable Noncontrolling Interest
Noncontrolling interest elimination (as a percent)											20.00%
Summit Materials, LLC | Davenport Assets
Equity Offering
Cash paid for acquisitions | $				450,000		$ 370,000
Summit Holdings LP
Redeemable Noncontrolling Interest
Number of LP Units outstanding								69,000,000
Voting power (as a percent)											100.00%
Noncontrolling interest elimination (as a percent)											3.20%	5.00%
Summit Materials, Inc. and Summit Holdings, LP
Equity Offering
Common stock issued (in shares)											10,000,000	1,038
Redeemable Noncontrolling Interest
Beginning Balance (in shares)											102,705,575	102,678,517
Issuance of Shares (in shares)											10,000,000	1,038
Other (in shares)											1,334,639	26,020
Ending Balance (in shares)											114,040,214	102,705,575	102,678,517
Common Class A
Equity Offering
Common stock, shares outstanding											110,350,594	96,033,222
Redeemable Noncontrolling Interest
Beginning Balance (in shares)											96,033,222
Ending Balance (in shares)											110,350,594	96,033,222
Dividend (in shares)		1,135,692	1,521,056
Common Class A | Continental Cement
Redeemable Noncontrolling Interest
Consideration, shares issued							1,029,183
Number of class units issued																100
Common Class A | Summit Holdings LP
Equity Offering
Common stock issued (in shares)											10,000,000	1,038
Redeemable Noncontrolling Interest
Beginning Balance (in shares)											97,554,278	52,402,692
Issuance of Shares (in shares)											10,000,000	1,038
Exchanges during period											1,461,677	45,124,528
Other (in shares)											1,334,639	26,020
Ending Balance (in shares)											110,350,594	97,554,278	52,402,692
Common Class B
Equity Offering
Common stock, shares outstanding											100	100
Redeemable Noncontrolling Interest
Beginning Balance (in shares)											100
Ending Balance (in shares)											100	100
Common Class B | Continental Cement
Redeemable Noncontrolling Interest
Number of class units issued																	100,000,000
Economic interest of redeemable noncontrolling interest, approximately																	30.00%
Ownership Percentage																	30.00%
10 1/2% Senior Notes, due 2020
Equity Offering
Senior notes, aggregate principal amount redeemed | $										$ 288,200				$ 153,800	$ 183,000
Senior notes, interest rate (as a percent)													10.50%
Non interest bearing notes payable | Continental Cement
Redeemable Noncontrolling Interest
Annual installments amount of non-interest bearing notes payable | $							$ 2,500
Number of annual installments | item							6
IPO
Equity Offering
Proceeds from sale of common stock, net of underwriting discounts | $								$ 433,000
IPO | Continental Cement
Equity Offering
Class B units purchased (in shares)							71,428,571
IPO | Affiliates of the Sponsors Blackstone Management Partners and Silverhawk Summit | Termination fee paid to related parties
Equity Offering
Related party expense | $							$ 13,800
IPO | Affiliates of the Sponsors Blackstone Management Partners and Silverhawk Summit | Summit Materials, LLC | Termination fee paid to related parties
Equity Offering
Related party expense | $							$ 13,800
IPO | Common Class A
Equity Offering
Common stock issued (in shares)								25,555,555
Offering price (in dollars per share) | $ / shares								$ 18.00
Redeemable Noncontrolling Interest
Issuance of Shares (in shares)								25,555,555
IPO | Common Class B
Equity Offering
Common stock issued (in shares)								69,007,297
Redeemable Noncontrolling Interest
Issuance of Shares (in shares)								69,007,297
IPO | 10 1/2% Senior Notes, due 2020
Equity Offering
Senior notes, aggregate principal amount redeemed | $										$ 288,200
Senior notes, interest rate (as a percent)										10.50%
Debt Instrument, redemption premium | $										$ 38,200
Accrued and unpaid interest | $										$ 5,200
Follow on Public Offering | Summit Holdings LP
Equity Offering
Number of Summit LP units purchased by Company, newly issued units (in shares)					3,750,000
Number of Summit LP units purchased by Company, from previous holders (in shares)					18,675,000
Follow on Public Offering | Davenport Assets
Equity Offering
Cash paid for acquisitions | $					$ 80,000
Redeemable Noncontrolling Interest
Number of terminals acquired (in facilities) | facility						7
Follow on Public Offering | Summit Materials, LLC | Davenport Assets
Equity Offering
Cash paid for acquisitions | $				$ 80,000
Follow on Public Offering | Common Class A
Equity Offering
Proceeds from sale of common stock, net of underwriting discounts | $	$ 237,600				$ 555,800
Common stock issued (in shares)	10,000,000				22,425,000
Offering price (in dollars per share) | $ / shares	$ 24.05				$ 25.75
Redeemable Noncontrolling Interest
Issuance of Shares (in shares)	10,000,000				22,425,000
LP Units
Redeemable Noncontrolling Interest
Number of LP Units outstanding											3,689,620	5,151,297	50,275,825
Number of LP Units exchanged											(1,461,677)	(45,124,528)