Amount of fee for an early repayment of debt.

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Debt instrument redemption charge. May include prepayment premium and write-off of deferred financing fees.

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Net benefit from write off original issuance premium and discount.

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Percentage of par value on senior notes.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Face (par) amount of the original debt instrument that was repurchased.

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

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Write-off of amounts previously capitalized as debt issuance cost in an extinguishment of debt.

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Debt - Senior Notes (Details) - USD ($)			3 Months Ended	12 Months Ended
Debt - Senior Notes (Details) - USD ($)	Mar. 15, 2019	Jun. 01, 2017	Mar. 30, 2019	Dec. 28, 2019	Dec. 30, 2017	Dec. 31, 2016	Jan. 02, 2016	Dec. 29, 2018	Nov. 30, 2015	Aug. 31, 2015	Apr. 30, 2015	Mar. 31, 2015
Debt
Long-term debt				$ 1,872,273,000				$ 1,828,159,000
Write off of deferred financing fees				2,850,000
8 1/2% Senior Notes, due 2022
Debt
Long-term debt				0				$ 250,000,000
Senior notes, interest rate (as a percent)								8.50%
5 1/8% Senior Notes, due 2025
Debt
Long-term debt				300,000,000				$ 300,000,000
6 1/8% Senior Notes, due 2023
Debt
Long-term debt				$ 649,133,000				648,891,000
Senior notes, interest rate (as a percent)				6.125%
10 1/2% Senior Notes, due 2020
Debt
Senior notes, interest rate (as a percent)												10.50%
Senior notes, aggregate principal amount redeemed									$ 153,800,000	$ 183,000,000.0	$ 288,200,000
Prepayment premium					$ 66,600,000
Write off of deferred financing fees					11,900,000
Charges on redemption						$ 56,500,000
Net benefit from the write-off the original issuance premium and discount					$ 22,000,000.0
Issuers \| 8 1/2% Senior Notes, due 2022
Debt
Senior notes, interest rate (as a percent)			8.50%
Loss on extinguishment of debt			$ (14,600,000)
Senior notes, aggregate principal amount redeemed			250,000,000.0
Prepayment premium			11,700,000
Write off of deferred financing fees			$ 2,900,000
Issuers \| 5 1/8% Senior Notes, due 2025
Debt
Long-term debt		$ 300,000,000.0
Senior notes, interest rate (as a percent)		5.125%
Percentage of par value of senior notes		100.00%
Proceeds net of related fees and expenses		$ 295,400,000
Issuers \| 6 1/8% Senior Notes, due 2023
Debt
Senior notes, interest rate (as a percent)							6.125%
Debt instrument, face amount							$ 650,000,000.0
Issuers \| 6 1/8% Senior Notes, due 2023, issued at par
Debt
Debt instrument, face amount							$ 350,000,000.0
Issuers \| 6 1/8% Senior Notes, due 2023, , issued at 99.375% of par
Debt
Percentage of par value of senior notes							99.375%
Debt instrument, face amount							$ 300,000,000.0
Summit Materials, LLC
Debt
Long-term debt				$ 1,872,273,000				1,828,159,000
Write off of deferred financing fees				2,850,000
Summit Materials, LLC \| 8 1/2% Senior Notes, due 2022
Debt
Long-term debt				0				$ 250,000,000
Senior notes, interest rate (as a percent)			8.50%					8.50%
Loss on extinguishment of debt			$ (14,600,000)
Senior notes, aggregate principal amount redeemed			250,000,000.0
Prepayment premium			11,700,000
Write off of deferred financing fees			$ 2,900,000
Summit Materials, LLC \| 5 1/8% Senior Notes, due 2025
Debt
Long-term debt		$ 300,000,000.0		$ 300,000,000				$ 300,000,000
Senior notes, interest rate (as a percent)		5.125%		5.125%
Percentage of par value of senior notes		100.00%
Proceeds net of related fees and expenses		$ 295,400,000
Summit Materials, LLC \| 6 1/8% Senior Notes, due 2023
Debt
Long-term debt				$ 649,133,000				648,891,000
Senior notes, interest rate (as a percent)				6.125%
Summit Materials, LLC \| 10 1/2% Senior Notes, due 2020
Debt
Senior notes, interest rate (as a percent)												10.50%
Senior notes, aggregate principal amount redeemed									$ 153,800,000	$ 183,000,000.0	$ 288,200,000
Prepayment premium						66,600,000
Write off of deferred financing fees						11,900,000
Charges on redemption						56,500,000
Net benefit from the write-off the original issuance premium and discount						$ 22,000,000.0
Senior Notes \| 6 1⁄2% Senior Notes, due 2027
Debt
Long-term debt				$ 300,000,000				0
Senior notes, interest rate (as a percent)				6.50%
Senior Notes \| Issuers \| 6 1⁄2% Senior Notes, due 2027
Debt
Long-term debt	$ 300,000,000.0
Senior notes, interest rate (as a percent)	6.50%
Percentage of par value of senior notes	100.00%
Proceeds net of related fees and expenses	$ 296,300,000
Senior Notes \| Summit Materials, LLC \| 6 1⁄2% Senior Notes, due 2027
Debt
Long-term debt				$ 300,000,000				$ 0
Senior notes, interest rate (as a percent)				6.50%