Condensed Financial Information Disclosure [Abstract] Condensed Financial Statements [Table] Condensed Financial Statements [Table] Consolidated Entities [Axis] Consolidated Entities [Axis] Consolidated Entities [Domain] Consolidated Entities [Domain] Issuers Subsidiary Issuer [Member] 100% Owned Guarantors Guarantor Subsidiaries [Member] Non-Guarantors Non-Guarantor Subsidiaries [Member] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Summit Materials, LLC Summit Materials Llc [Member] Summit Materials, LLC, a wholly owned indirect subsidiary of the registrant. Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Reportable Legal Entities Reportable Legal Entities [Member] Eliminations Consolidation, Eliminations [Member] Condensed Consolidating Statements of Operations Condensed Financial Statements, Captions [Line Items] Revenue Revenue from Contract with Customer, Excluding Assessed Tax Cost of revenue (excluding items shown separately below) Cost of Goods and Services Sold General and administrative expenses General Administrative And Other Expenses General, administrative and other expenses. Depreciation, depletion, amortization and accretion Depreciation Depletion Amortization And Accretion The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, depleting assets or accretion of asset retirement obligations to periods that benefit from use of the related assets. Operating income Operating Income (Loss) Other (income) loss, net Other Nonoperating Income Expense Net Other Nonoperating Income Expense Net Interest expense (income) Interest Income (Expense), Net Gain on sale of business Gain (Loss) on Disposition of Business Income from operations before taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Income tax expense Income Tax Expense (Benefit) Net income attributable to Summit Inc. Net Income (Loss) Available to Common Stockholders, Basic Comprehensive income attributable to member of Summit Materials, LLC Comprehensive Income (Loss), Net of Tax, Attributable to Parent Goodwill and Intangible Assets Disclosure [Abstract] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Business Acquisition [Line Items] Business Acquisition [Line Items] Goodwill and Intangibles Goodwill and Intangible Assets Disclosure [Text Block] Payables and Accruals [Abstract] Accrued Expenses [Table] Accrued Expenses [Table] Accrued Expenses [Table] Schedule Of Accrued Expenses [Line Items] Schedule Of Accrued Expenses [Line Items] Schedule Of Accrued Expenses [Line Items] Interest Interest Payable, Current Payroll and benefits Accrued Employee Benefits, Current Finance lease obligations Finance Lease, Liability, Current Finance lease obligations Capital Lease Obligations, Current Insurance Accrued Insurance, Current Non-income taxes Accrual for Taxes Other than Income Taxes, Current Professional fees Accrued Professional Fees, Current Other Other Accrued Liabilities, Current Total Accrued Liabilities, Current Debt Disclosure [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Debt Instrument [Line Items] Debt Instrument [Line Items] Deferred Finance Costs, Own-share Lending Arrangement, Issuance Costs, Accumulated Amortization [Roll Forward] Deferred Finance Costs, Own-share Lending Arrangement, Issuance Costs, Accumulated Amortization [Roll Forward] Beginning balance Debt Issuance Costs, Net Loan origination fees Payments of Debt Issuance Costs Amortization Amortization of Debt Issuance Costs Write off of deferred financing fees Write off of Deferred Debt Issuance Cost Ending balance Income Tax Disclosure [Abstract] Income Taxes [Table] Income Taxes [Table] Income Taxes [Table] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Class A Common Stock Common Class A [Member] Summit Holdings LP Summit Holdings Lp [Member] Summit Materials Holdings L.P., a non-wholly owned subsidiary of the registrant. Collaborative Arrangement and Arrangement Other than Collaborative [Axis] Collaborative Arrangement and Arrangement Other than Collaborative [Axis] Collaborative Arrangement and Arrangement Other than Collaborative [Domain] Collaborative Arrangement and Arrangement Other than Collaborative [Domain] Tax Receivable Agreement Tax Receivable Agreement [Member] Information pertaining to the tax receivable agreement. Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Accrued expenses. Accounts Payable and Accrued Liabilities [Member] Income Taxes [Line Items] Income Taxes [Line Items] Income Taxes [Line Items] Income tax expense Valuation Allowance Valuation Allowance [Abstract] Valuation allowance Deferred Tax Assets, Valuation Allowance Income tax provision, interest or penalties recognized Income Tax Examination, Penalties and Interest Expense Percentage of benefits to be paid on tax receivable agreement Percentage Of Tax Receivable Agreement Percentage of benefits related to tax receivable agreement paid by entity. Exchanges during period (in shares) Stock Issued During Period, Shares, Conversion of Units Deferred tax asset, Investment in limited partnership Deferred Tax Assets, Investments Tax receivable agreement liability Tax Receivable Agreement Liability Represents the liability due to former holders of LP Units related to the Tax Receivable Agreement. Distributions to LP Unitholders Limited Partners' Capital Account, Distribution Amount Supplemental Cash Flow Elements [Abstract] Schedule Of Cash Flow Supplemental [Table] Schedule Of Cash Flow Supplemental [Table] Schedule Of Cash Flow Supplemental [Table] Schedule Of Cash Flow Supplemental [Line Items] Schedule Of Cash Flow Supplemental [Line Items] 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. Schedule of Supplemental Cash Flow Information Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Amortization expense Amortization of Intangible Assets Estimated amortization expense Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract] 2019 (three months) Finite-Lived Intangible Assets, Amortization Expense, Remainder of Fiscal Year 2020 Finite-Lived Intangible Assets, Amortization Expense, Year Two 2021 Finite-Lived Intangible Assets, Amortization Expense, Year Three 2022 Finite-Lived Intangible Assets, Amortization Expense, Year Four 2023 Finite-Lived Intangible Assets, Amortization Expense, Year Five 2024 Finite Lived Intangible Assets Amortization Expense Year Six Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the sixth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Thereafter Finite Lived Intangible Assets Amortization Expense After Year Six Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized after the sixth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. Total Finite-Lived Intangible Assets, Net Earnings Per Share [Abstract] Schedule of Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Table] Schedule of Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Table] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] LP Units Limited Partnership Units [Member] Units representing ownership interest in a limited partnership (LP). Stock options Share-based Payment Arrangement, Option [Member] Warrants Warrant [Member] Restricted Stock Units (RSUs) [Member] Restricted Stock Units (RSUs) [Member] Performance Shares [Member] Performance Shares [Member] Reconciliation of basic to diluted loss per share Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] Net income attributable to Summit Inc. Weighted average shares of Class A stock outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Basic earnings per share (usd per share) Earnings Per Share, Basic and Diluted Diluted net income attributable to Summit Inc. Net Income (Loss) Attributable to Parent, Diluted Weighted average shares of Class A stock outstanding (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Weighted average shares of Class A stock outstanding (in shares) Incremental Common Shares Attributable to Dilutive Effect of Call Options and Warrants Weighted average dilutive shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Diluted Diluted earnings per share (usd per share) Earnings Per Share, Diluted Anti dilutive shares excluded from calculation of earnings per share (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Accounting Policies [Abstract] Schedule Of Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Table] Schedule Of Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Table] Schedule Of Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Table] Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items] Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items] Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items] Summary of Organization and Significant Accounting Policies Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Fair Value Disclosures [Abstract] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Schedule of Contingent Consideration and Derivatives Measured at Fair Value Fair Value, Liabilities Measured on Recurring and Nonrecurring Basis [Table Text Block] Schedule of Carrying Value and Fair Value of Financial Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Members' equity Member Units [Member] Accumulated Earnings (Deficit) Retained Earnings [Member] Accumulated other comprehensive income (loss) AOCI Attributable to Parent [Member] Common Stock Common Stock [Member] Additional Paid-in Capital Additional Paid-in Capital [Member] Noncontrolling Interest in Summit Holdings Noncontrolling Interest In Lp [Member] Noncontrolling interest attributable to the ownership in Summit Materials Holdings, L.P., of which Summit Materials, LLC is a an indirect wholly owned subsidiary. Class B Common Stock Common Class B [Member] Statement [Line Items] Statement [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Beginning balance Limited Liability Company (LLC) Members' Equity, Including Portion Attributable to Noncontrolling Interest Beginning balance (in shares) Common Stock, Shares, Issued Net contributed capital Contribution To Members Equity Capital contributed to limited liability company (LLC). Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest LP Unit exchanges (in shares) LP Unit exchanges Stock Issued During Period, Value, Conversion of Units Other comprehensive income, net of tax Other Comprehensive Income (Loss), Net of Tax Stock option exercises (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Stock option exercises Stock Issued During Period, Value, Stock Options Exercised Distributions Distribution Made to Limited Liability Company (LLC) Member, Cash Distributions Declared Share-based compensation APIC, Share-based Payment Arrangement, Increase for Cost Recognition Distributions from partnership Partners' Capital Account, Distributions Shares redeemed to settle taxes and other (in shares) Other Equity Activity, Shares Represents other stockholder equity activity, in shares. Shares redeemed to settle taxes and other Other Equity Activity, Value Represents other stockholder equity activity. Ending balance Ending balance Ending balance (in shares) 2019 (three months) Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year 2020 Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months 2021 Long-term Debt, Maturities, Repayments of Principal in Year Two 2022 Long-term Debt, Maturities, Repayments of Principal in Year Three 2023 Long-term Debt, Maturities, Repayments of Principal in Year Four 2024 Long-term Debt, Maturities, Repayments of Principal in Year Five Thereafter Long-term Debt, Maturities, Repayments of Principal after Year Five Total Long-term Debt, Gross Less: Original issue net discount Debt Instrument, Unamortized Discount Less: Capitalized loan costs Deferred Costs Total debt Long-term Debt, Net Carrying amount of long-term debt, net of unamortized discount or premium and debt issuance costs, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. Leases [Abstract] Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Schedule of Lease Cost Lease, Cost [Table Text Block] Schedule of Lease Assets and Liabilities Assets And Liabilities, Lessee [Table Text Block] Assets And Liabilities, Lessee [Table Text Block] Schedule of Finance Lease Liability Maturities Finance Lease, Liability, Maturity [Table Text Block] Schedule of Operating Lease Liability Maturities Lessee, Operating Lease, Liability, Maturity [Table Text Block] Schedule of Future Minimum Rental Payments for Operating Leases Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Senior Notes Senior Notes [Member] Issuers Summit Materials Llc And Summit Materials Finance Corp [Member] Information pertaining to Summit Materials, LLC and Summit Materials Finance Corp. (collectively, the "Issuers"). Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] 6 1/2% Senior Notes, due 2027 Six Point Five Percentage Senior Notes Due Twenty Twenty Seven [Member] Six Point Five Percentage Senior Notes Due Twenty Twenty Seven [Member] 8 1/2% Senior Notes, due 2022 Senior Notes8.5 Percent Due2022 [Member] Represents 8.5 percent senior notes of the entity due in 2022. 5 1/8% Senior Notes, due 2025 Five Point One Two Five Percentage Senior Notes Due Twenty Twenty Five [Member] Represents the 5.125 percent senior notes of the entity due in 2025. 6 1/8% Senior Notes, due 2023 Six Point One Two Five Percentage Senior Notes Due Twenty Twenty Three [Member] Represents 6.125 percent senior notes of the entity due in 2023. 6 1/8% Senior Notes, due 2023, issued at par Six Point One Two Five Percentage Senior Notes Due Twenty Twenty Three Issued At Par [Member] Represents 6.125 percent senior notes of the entity due in 2023, issued at par. 6 1/8% Senior Notes, due 2023, issued at 99.375% of par Six Point One Two Five Percentage Senior Notes Due Twenty Twenty Three Issued At99.375 Percent Of Par [Member] Represents 6.125 percent senior notes of the entity due in 2023, issued at 99.375 percent of par. Long-term debt Long-term Debt Senior notes, interest rate (as a percent) Debt Instrument, Interest Rate, Stated Percentage Percentage of par value of senior notes Percentage Of Par Value On Senior Notes Percentage of par value on senior notes. Proceeds net of related fees and expenses Proceeds from Debt, Net of Issuance Costs Debt instrument, repurchased face amount Debt Instrument, Repurchased Face Amount Debt instrument redemption charge Gain (Loss) on Extinguishment of Debt Debt instrument, prepayment premium Debt Instrument, Prepayment Premium Amount of fee for an early repayment of debt. Write off of deferred financing fees Debt instrument, face amount Debt Instrument, Face Amount Segment Reporting [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Operating segment Operating Segments [Member] Corporate, Non-Segment Corporate, Non-Segment [Member] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] West West [Member] Represents the west region segment of the reporting entity. East East [Member] Represents the east region segment of the reporting entity. Cement Cement [Member] Represents the cement segment of the reporting entity. Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Number of operating segments Number of Operating Segments Number of reportable segments Number of Reportable Segments Total revenue Interest expense Interest Expense Depreciation, depletion and amortization Depreciation, Depletion and Amortization Accretion Asset Retirement Obligation, Accretion Expense Loss on debt financings Gain Loss On Debt Financing Gain loss on debt financing. Gain on sale of business Transaction costs Business Combination, Acquisition Related Costs Non-cash compensation Non Cash Compensation Expense Non Cash Compensation Expense Other Miscellaneous Other Income (Expense) Miscellaneous other income (expense). Total Adjusted EBITDA Adjusted Earnings Before Interest Income Taxes Depreciation And Amortization Adjusted earnings before interest, income taxes, depreciation and amortization (Adjusted EBITDA). Total purchases of property, plant and equipment Payments to Acquire Property, Plant, and Equipment Total depreciation, depletion, amortization and accretion Total assets Assets Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Level 2 Fair Value, Inputs, Level 2 [Member] Level 3 Fair Value, Inputs, Level 3 [Member] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] Carrying Value Reported Value Measurement [Member] Financial Instruments Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Long-term debt Long-term Debt, Fair Value Current portion of deferred consideration and noncompete obligations Deferred Consideration and Noncompete Obligations Current Fair Value Disclosure Deferred consideration and noncompete obligations current fair value. Long term portion of deferred consideration and noncompete obligations Deferred Consideration and Noncompete Obligations Noncurrent Fair Value Disclosure Deferred consideration and noncompete obligations noncurrent fair value. Current portion of debt Long-term Debt, Current Maturities Statement of Financial Position [Abstract] Assets Assets [Abstract] Current assets: Assets, Current [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Accounts receivable, net Accounts Receivable, after Allowance for Credit Loss, Current Costs and estimated earnings in excess of billings Contract with Customer, Asset, Net, Current Inventories Inventory, Net Other current assets Other Assets, Current Total current assets Assets, Current Property, plant and equipment, less accumulated depreciation, depletion and amortization (September 28, 2019 - $923,439 and December 29, 2018 - $794,251) Property, Plant and Equipment, Net Goodwill Goodwill Intangible assets, less accumulated amortization (September 28, 2019 - $9,666 and December 29, 2018 - $8,247) Deferred tax assets, less valuation allowance (September 28, 2019 - $29,472 and December 29, 2018 - $19,366) Deferred Income Tax Assets, Net Operating lease right-of-use assets Operating Lease, Right-of-Use Asset Other assets Other Assets, Noncurrent Total assets Liabilities and Stockholders’ Equity/Member's Interest Liabilities and Equity [Abstract] Current liabilities: Liabilities, Current [Abstract] Current portion of debt Debt, Current Current portion of acquisition-related liabilities Acquisition Related Liabilities Current The amount of consideration for a business acquisition due in the current period. Accounts payable Accounts Payable, Current Accrued expenses Current operating lease liabilities Operating Lease, Liability, Current Billings in excess of costs and estimated earnings Contract with Customer, Liability, Current Total current liabilities Liabilities, Current Long-term debt Long Term Debt Noncurrent, Net Carrying amount of long-term debt, after unamortized (discount) premium and debt issuance costs, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities). Acquisition-related liabilities Acquisition Related Liabilities Non Current The amount of consideration for a business acquisition that is not due in the next twelve months. Noncurrent operating lease liabilities Operating Lease, Liability, Noncurrent Other noncurrent liabilities Other Liabilities, Noncurrent Total liabilities Liabilities Commitments and contingencies (see note 12) Commitments and Contingencies Stockholders’ equity/Member's interest Stockholders' Equity Attributable to Parent [Abstract] Common stock Common Stock, Value, Issued Members' equity Members' Capital Additional paid-in capital Additional Paid in Capital, Common Stock Accumulated earnings Retained Earnings (Accumulated Deficit) Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax Stockholders’ equity Stockholders' Equity Attributable to Parent Noncontrolling interest in Summit Holdings Stockholders' Equity Attributable to Noncontrolling Interest, Excluding Portion Attributable To Noncontrolling Interest Of Wholly Owned Indirect Subsidiary Of Registrant Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which is directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent (that is, noncontrolling interest, previously referred to as minority interest), excluding portion attributable to noncontrolling interest of the wholly owned indirect subsidiary of the registrant. Total member's interest Total stockholders’ equity Total liabilities and stockholders’ equity/member's interest Liabilities and Equity Income Statement [Abstract] Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] Product Product [Member] Service Service [Member] Excluding delivery and subcontract revenue Excluding Shipping And Handling [Member] Excluding Shipping And Handling [Member] Delivery and subcontract revenue Shipping and Handling [Member] Revenue: Revenue from Contract with Customer [Abstract] Cost of revenue (excluding items shown separately below): Cost of Goods and Services Sold [Abstract] Net cost of revenue General and administrative expenses General and Administrative Expense Other income, net Other Nonoperating Income (Expense) Net income Net income attributable to Summit Holdings Net Income Loss Attributable To Noncontrolling Interest, Excluding Portion Attributable To Noncontrolling Interest Of Wholly Owned Indirect Subsidiary Of Registrant Amount of Net Income (Loss) attributable to noncontrolling interest, excluding portion attributable to noncontrolling interest of the wholly owned indirect subsidiary of the registrant. Earnings per share of Class A common stock: Basic (usd per share) Earnings Per Share, Basic Diluted (usd per share) Weighted average shares of Class A common stock: Weighted Average Number of Shares Outstanding, Diluted [Abstract] Basic (in shares) Diluted (in shares) Inventory Disclosure [Abstract] Inventory, Current [Table] Inventory, Current [Table] Inventory [Line Items] Inventory [Line Items] Components of Inventories Schedule of Inventory, Current [Table Text Block] Commitments and Contingencies Disclosure [Abstract] Loss Contingencies [Table] Loss Contingencies [Table] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] LEASES Lessee, Operating Leases [Text Block] LEASES Lessee, Finance Leases [Text Block] Stockholders' Equity Note [Abstract] Schedule of Capitalization, Equity [Table] Schedule of Capitalization, Equity [Table] Schedule of Capitalization, Equity [Line Items] Schedule of Capitalization, Equity [Line Items] Schedule of changes in ownership of Summit Holdings Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Table Text Block] Schedule of Changes in Each Component of Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Income Taxes Income Tax Disclosure [Text Block] Earnings Per Share Earnings Per Share [Text Block] Debt Debt Disclosure [Text Block] Goodwill by Reportable Segment and in Total Schedule of Goodwill [Table Text Block] Intangible Assets by Type and in Total Schedule of Finite-Lived Intangible Assets [Table Text Block] Estimated Amortization Expense for Intangible Assets Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Segment Information Segment Reporting Disclosure [Text Block] Schedule of Basic Earnings Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Statistical Measurement [Axis] Statistical Measurement [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] Maximum Maximum [Member] Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Trade accounts receivable Trade Accounts Receivable Trade receivable amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services. Construction contract receivables Billed Contracts Receivable Retention receivables Retention Receivables Amounts earned by entity but held by customers until projects have been fully completed or near completion and are expected to be billed and collected within one year of the balance sheet date (or the normal operating cycle, whichever is longer). Receivables from related parties Accounts Receivable, Related Parties Accounts receivable Accounts Receivable, before Allowance for Credit Loss, Current Less: Allowance for doubtful accounts Accounts Receivable, Allowance for Credit Loss, Current Accounts receivable, net General collection and billing period for retention receivables Collection and Billing Period, Retention Receivables The general collection and billing period for retention receivables. Measurement Input Type [Axis] Measurement Input Type [Axis] Measurement Input Type [Domain] Measurement Input Type [Domain] Discount Rate Measurement Input, Discount Rate [Member] Hedging Relationship [Axis] Hedging Relationship [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Cash flow hedges Cash Flow Hedging [Member] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Interest rate derivatives Interest Rate Contract [Member] Term Loan, due 2022 Senior Secured Credit Facility Term Loan Due Two Thousand Twenty Two [Member] Represents term loan of the entity due in 2022 under the entity's Senior Secured Credit Facility. Term loan borrowings hedged by derivatives Derivative, Amount of Hedged Item Current portion of acquisition-related liabilities and accrued expenses - contingent consideration Business Combination, Contingent Consideration, Liability, Current Current portion of acquisition-related liabilities and accrued expenses - cash flow hedge Derivative Liability, Current Acquisition-related liabilities and other noncurrent liabilities - contingent consideration Business Combination, Contingent Consideration, Liability, Noncurrent Acquisition-related liabilities and other noncurrent liabilities - cash flow hedge Derivative Liability, Noncurrent Contingent consideration fair value measurement input Business Combination, Contingent Consideration, Liability, Measurement Input Adjustment to contingent consideration Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability Accumulated depreciation, depletion and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization Common stock, par value (usd per share) Common Stock, Par or Stated Value Per Share Common stock, shares authorized (in shares) Common Stock, Shares Authorized Common stock, shares issued (in shares) Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Ownership [Axis] Ownership [Axis] Ownership [Domain] Ownership [Domain] Summit Materials Inc [Member] Summit Materials Inc [Member] Summit Materials Inc [Member] Capital Units by Class [Axis] Capital Units by Class [Axis] Capital Unit, Class [Domain] Capital Unit, Class [Domain] LP Units Lp Units [Member] Lp Units [Member] Summit Materials, Inc. and Summit Holdings, LP Summit Materials Incorporated And Summit Holdings L P [Member] Information pertaining to Summit Materials, Inc. and Summit Holdings, LP. Other equity transactions (in shares) Number of LP Units outstanding, beginning balance (in shares) Limited Partners' Capital Account, Units Outstanding Number of LP Units exchanged (in shares) Limited Partners' Capital Account, Units Exchanged The number of limited partner units exchanged. Number of LP Units outstanding, ending balance (in shares) Ownership percentage Noncontrolling Interest, Ownership Percentage by Parent Noncontrolling interest elimination (as a percent) Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Mineral leases Lease Agreements [Member] Reserve rights Reserve Rights [Member] Reserve rights. Trade names Trade Names [Member] Other Other Intangible Assets [Member] Finite-Lived Intangible Assets [Line Items] Gross Carrying Amount Intangible Assets, Gross (Excluding Goodwill) Accumulated Amortization Net Carrying Amount Intangible Assets, Net (Excluding Goodwill) Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] Prime rate Prime Rate [Member] Canadian subsidiary credit agreement, Operating activities Canadian Subsidiary Credit Agreement Operating Activities [Member] Represents information pertaining to credit agreement of wholly-owned Canadian subsidiary to be used for operating activities. Canadian subsidiary credit agreement, Capital equipment Canadian Subsidiary Credit Agreement Capital Equipment [Member] Represents information pertaining to credit agreement of wholly-owned Canadian subsidiary to be used for capital equipment. Canadian subsidiary credit agreement, Guarantees Canadian Subsidiary Credit Agreement Guarantees [Member] Represents information pertaining to credit agreement of wholly-owned Canadian subsidiary to provide guarantees on behalf of that subsidiary. Canadian subsidiary credit agreement Canadian Subsidiary Credit Agreement [Member] Represents information pertaining to credit agreement of wholly-owned Canadian subsidiary. Revolving credit commitment Line of Credit Facility, Maximum Borrowing Capacity Basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate Amount outstanding Long-term Line of Credit Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Proceeds from sale of business Proceeds from Divestiture of Businesses Gain on sale of business Operating lease liability Operating Lease, Liability Cover page. Document Information [Table] Document Information [Table] Document Information [Line Items] Document Information [Line Items] Document Type Document Type Document Quarterly Report Document Quarterly Report Document Period End Date Document Period End Date Document Transition Report Document Transition Report Entity File Number Entity File Number Entity Registrant Name Entity Registrant Name Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Tax Identification Number Entity Tax Identification Number Entity Address, Address Line One Entity Address, Address Line One Entity Address, Address Line Two Entity Address, Address Line Two Entity Address, City or Town Entity Address, City or Town Entity Address, State or Province Entity Address, State or Province Entity Address, Postal Zip Code Entity Address, Postal Zip Code City Area Code City Area Code Local Phone Number Local Phone Number Title of 12(b) Security Title of 12(b) Security Trading Symbol Trading Symbol Security Exchange Name Security Exchange Name Entity Current Reporting Status Entity Current Reporting Status Entity Interactive Data Current Entity Interactive Data Current Entity Filer Category Entity Filer Category Entity Small Business Entity Small Business Entity Emerging Growth Company Entity Emerging Growth Company Entity Shell Company Entity Shell Company Entity common stock, shares outstanding (in shares) Entity Common Stock, Shares Outstanding Entity Central Index Key Entity Central Index Key Amendment Flag Amendment Flag Current Fiscal Year End Date Current Fiscal Year End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Accrued Expenses Accounts Payable and Accrued Liabilities Disclosure [Text Block] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Change in retirement plans Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Foreign currency translation adjustments Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Cash flow hedge adjustments Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Changes in each component of accumulated other comprehensive loss AOCI Attributable to Parent, Net of Tax [Roll Forward] Beginning balance Foreign currency translation adjustment, net of tax Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent (Loss) income on cash flow hedges, net of tax Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax Ending balance Supplemental Cash Flow Information Cash Flow, Supplemental Disclosures [Text Block] Intercompany receivables Intercompany Receivables Assets Current Intercompany Receivables Assets Current Cost and estimated earnings in excess of billings Property, plant and equipment, net Intangible assets, net Liabilities and Member’s Interest Intercompany payables Intercompany Payables Liabilities Current Intercompany Payables Liabilities Current Total member's interest Concentration Risk [Table] Concentration Risk [Table] Business and Credit Concentrations Concentration Risk [Line Items] Number of states in which the entity operates Number of States in which Entity Operates Percentage of the tax receivable agreement allocated to additional paid-in capital Tax Receivable Agreement, Additional Paid in Capital, Percent The percentage of the tax receivable agreement allocated to additional paid-in capital. Schedule of Debt Schedule of Debt [Table Text Block] Schedule of Contractual Payments of Long-Term Debt Schedule of Maturities of Long-term Debt [Table Text Block] Summary of Activity for Deferred Financing Fees Schedule Of Deferred Financing Fees [Table Text Block] Schedule of deferred financing fees. Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Principles of Consolidation Consolidation, Policy [Policy Text Block] Use of Estimates Use of Estimates, Policy [Policy Text Block] Business and Credit Concentrations Concentration Risk, Credit Risk, Policy [Policy Text Block] Revenue Recognition Revenue from Contract with Customer [Policy Text Block] Earnings per Share Earnings Per Share, Policy [Policy Text Block] Tax Receivable Agreement Tax Receivable Agreement [Policy Text Block] Disclosure of accounting policy for tax receivable agreement. New Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Leases Lessee, Leases [Policy Text Block] Components of Accrued Expenses Schedule of Accrued Liabilities [Table Text Block] Lease, Cost [Abstract] Lease, Cost [Abstract] Operating lease cost Operating Lease, Cost Variable lease cost Variable Lease, Cost Short-term lease cost Short-term Lease, Cost Financing lease cost: Finance Lease Cost1 [Abstract] Finance Lease Cost1 [Abstract] Amortization of right-of-use assets Finance Lease, Right-of-Use Asset, Amortization Interest on lease liabilities Finance Lease, Interest Expense Total lease cost Lease, Cost Supplemental balance sheet information related to leases: Assets and Liabilities, Lessee [Abstract] Operating leases: Operating Leases [Abstract] Operating Leases [Abstract] Total operating lease liabilities Finance leases: Finance Leases [Abstract] Finance Leases [Abstract] Property and equipment, gross Finance Lease, Right-Of-Use Asset, Gross Finance Lease, Right-Of-Use Asset, Gross Less accumulated depreciation Finance Lease, Right-Of-Use Asset, Accumulated Amortization Finance Lease, Right-Of-Use Asset, Accumulated Amortization Property and equipment, net Finance Lease, Right-of-Use Asset Current finance lease liabilities Long-term finance lease liabilities Finance Lease, Liability, Noncurrent Total finance lease liabilities Finance Lease, Liability Weighted average: Weighted Average Lease Term And Discount Rate [Abstract] Weighted Average Lease Term And Discount Rate [Abstract] Lease Term Lease Term [Abstract] Lease Term [Abstract] Operating leases Operating Lease, Weighted Average Remaining Lease Term Finance lease Finance Lease, Weighted Average Remaining Lease Term Discount Rate Lease Discount Rate [Abstract] Lease Discount Rate [Abstract] Operating leases Operating Lease, Weighted Average Discount Rate, Percent Finance lease Finance Lease, Weighted Average Discount Rate, Percent Operating Leases Lessee, Operating Lease, Liability, Payment, Due [Abstract] 2019 (three months) Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year 2020 Lessee, Operating Lease, Liability, Payments, Due Year Two 2021 Lessee, Operating Lease, Liability, Payments, Due Year Three 2022 Lessee, Operating Lease, Liability, Payments, Due Year Four 2023 Lessee, Operating Lease, Liability, Payments, Due Year Five 2024 Lessee, Operating Lease, Liability, Payments, Due Year Six Lessee, Operating Lease, Liability, Payments, Due Year Six Thereafter Lessee, Operating Lease, Liability, Payments, Due After Year Six Lessee, Operating Lease, Liability, Payments, Due After Year Six Total lease payments Lessee, Operating Lease, Liability, Payments, Due Less imputed interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Finance Leases Finance Lease, Liability, Payment, Due [Abstract] 2019 (three months) Finance Lease, Liability, Payments, Remainder of Fiscal Year 2020 Finance Lease, Liability, Payments, Due Year Two 2021 Finance Lease, Liability, Payments, Due Year Three 2022 Finance Lease, Liability, Payments, Due Year Four 2023 Finance Lease, Liability, Payments, Due Year Five 2024 Finance Lease, Liability, Payments, Due Year Six Finance Lease, Liability, Payments, Due Year Six Thereafter Finance Lease, Liability, Payments, Due After Year Six Finance Lease, Liability, Payments, Due After Year Six Total lease payments Finance Lease, Liability, Payment, Due Less imputed interest Finance Lease, Liability, Undiscounted Excess Amount Term Loan, due 2024 Senior Secured Credit Facility Term Loan Due Two Thousand Twenty Four [Member] Represents term loan of the entity due in 2024 under the entity's Senior Secured Credit Facility. Total debt Current portion of long-term debt Long-term debt Long-term Debt, Excluding Current Maturities Gross amount Debt discount Debt instrument interest rate (as a percent) Net cash (used in) provided by operating activities Net Cash Provided by (Used in) Operating Activities Cash flow from investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Acquisitions, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Purchase of property, plant and equipment Proceeds from the sale of property, plant, and equipment Proceeds from Sale of Property, Plant, and Equipment Proceeds from the sale of a business Other Payments for (Proceeds from) Other Investing Activities Net cash used for investing activities Net Cash Provided by (Used in) Investing Activities Cash flow from financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Proceeds from investment by member Proceeds from (Repayments) of Partnership Contribution The cash inflow (outflow) from capital received or paid in cash from a partner in a partnership during the period. Net proceeds from debt issuance Proceeds from Issuance of Debt Loans received from and payments made on loans from other Summit Companies Proceeds from (Repayments of) Related Party Debt Payments on long-term debt Repayments of Debt Payments on acquisition-related liabilities Payments of Merger Related Costs, Financing Activities Debt issuance costs Payments of Financing Costs Distributions from partnership Payments of Distributions to Affiliates Other Proceeds from (Payments for) Other Financing Activities Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Impact of cash on foreign currency Effect of Exchange Rate on Cash and Cash Equivalents Net increase (decrease) in cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Cash and cash equivalents—beginning of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash and cash equivalents—end of period Cash payments: Supplemental Cash Flow Information [Abstract] Interest Interest Paid, Excluding Capitalized Interest, Operating Activities (Refund) payments for income taxes, net Income Taxes Paid, Net Operating cash payments on operating leases Operating Lease, Payments Operating cash payments on finance leases Finance Lease, Interest Payment on Liability Non cash financing activities: Finance Lease, Principal Payments Right of use assets obtained in exchange for finance leases obligations Non Cash Financing Activities [Abstract] Non Cash Financing Activities [Abstract] Right of use assets obtained in exchange for operating lease obligations Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Right of use assets obtained in exchange for finance leases obligations Right-of-Use Asset Obtained in Exchange for Finance Lease Liability Exchange of LP Units to shares of Class A common stock Conversion of Stock, Amount Converted Inventories Inventory Disclosure [Text Block] Aggregate stockpiles Inventory, Ore Stockpiles on Leach Pads, Gross Finished goods Inventory, Finished Goods, Net of Reserves Work in process Inventory, Work in Process, Net of Reserves Raw materials Inventory, Raw Materials, Net of Reserves Total Statement of Cash Flows [Abstract] Cash flow from operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Net income Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation, depletion, amortization and accretion Depreciation Depletion Amortization And Accretion On Asset Retirement Obligation Depreciation depletion amortization and accretion on asset retirement obligation. Share-based compensation expense Share-based Payment Arrangement, Noncash Expense Net gain on asset disposals Gain (Loss) on Disposition of Assets Non-cash loss on debt financings Non Cash Gain Loss On Debt Refinancing Non-cash loss on debt refinancing. Change in deferred tax asset, net Deferred Income Taxes and Tax Credits Other Other Noncash Income (Expense) (Increase) decrease in operating assets, net of acquisitions and dispositions: Increase (Decrease) in Operating Assets [Abstract] Accounts receivable, net Increase (Decrease) in Accounts Receivable Inventories Increase (Decrease) in Inventories Costs and estimated earnings in excess of billings Contract With Customer, Asset, Cumulative Catch-up Adjustment To Revenue, Change In Revenue Billed, Contract Price Or Estimates Amount of increase (decrease) in revenue recognized for cumulative catch-up adjustment from change in revenue billed, contract price or cost estimates which increases (decreases) right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time. Other current assets Increase (Decrease) in Other Current Assets Other assets Increase (Decrease) in Other Noncurrent Assets (Decrease) increase in operating liabilities, net of acquisitions and dispositions: Increase (Decrease) in Operating Liabilities [Abstract] Accounts payable Increase (Decrease) in Accounts Payable Accrued expenses Increase (Decrease) in Accrued Liabilities Billings in excess of costs and estimated earnings Contract With Customer, Liability, Cumulative Catch-up Adjustment To Revenue, Change In Revenue Billed, Contract Price Or Cost Estimates Amount of increase (decrease) in revenue recognized for cumulative catch-up adjustment from change in revenue billed, contract pric or cost estimates which (increases) decreases obligation to transfer good or service to customer for which consideration from customer has been received or is due. Includes, but is not limited to, change in assessment of whether estimate of variable consideration is constrained. Tax receivable agreement liability Increase (Decrease) in Tax Receivable Agreement Liability Amount of increase (decrease) in tax receivable agreement liability. Other liabilities Increase (Decrease) in Other Operating Liabilities Net cash provided by operating activities Purchases of property, plant and equipment Proceeds from the sale of property, plant and equipment Net cash used for investing activities Capital contributions by member Proceeds from Partnership Contribution Proceeds from debt issuances Debt issuance costs Payments on debt Proceeds from stock option exercises Proceeds from Stock Options Exercised Impact of foreign currency on cash Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Net increase (decrease) in cash Summary of Financial Data for Company's Reportable Business Segments Schedule of Segment Reporting Information, by Segment [Table Text Block] Revolving Credit Facility Senior Secured Credit Facility Revolving Credit Facility [Member] Represents revolving credit facility under the entity's Senior Secured Credit Facility. Letter of Credit Senior Secured Credit Facility Letter Of Credit [Member] Represents letters of credit under the entity's Senior Secured Credit Facility. Senior Secured Credit Facilities Senior Secured Credit Facilities [Member] Represents Senior Secured Credit Facilities of the entity. Federal funds rate Federal Funds Effective Rate [Member] Interest rate at which a depository institution lends funds maintained at the Federal Reserve to another depository institution overnight. LIBOR Plus 1% London Interbank Offered Rate Libor Plus One Percent [Member] Interest rate at which a bank borrows funds from other banks in the London interbank market plus one percent. LIBOR London Interbank Offered Rate (LIBOR) [Member] Maximum borrowing capacity Quarterly principal repayments percentage Debt Instrument Quarterly Principal Repayment Percentage Represents the required quarterly principal repayments of debt as a percent. Basis spread on variable rate Percentage added to base rate Debt Instrument, Reference Rate, Additional Percentage Percentage points added to the base rate to determine reference rate. Remaining borrowing capacity Line of Credit Facility, Remaining Borrowing Capacity First lien leverage ratio First Lien Leverage Ratio First lien leverage ratio as defined in the terms of the agreement. 2019 Operating Leases, Future Minimum Payments Due, Next Twelve Months 2020 Operating Leases, Future Minimum Payments, Due in Two Years 2021 Operating Leases, Future Minimum Payments, Due in Three Years 2022 Operating Leases, Future Minimum Payments, Due in Four Years 2023 Operating Leases, Future Minimum Payments, Due in Five Years Revenue from External Customers by Products and Services [Table] Revenue from External Customers by Products and Services [Table] Aggregates Aggregates [Member] Aggregates. Ready-mix concrete Ready Mixed Concrete [Member] Ready mixed concrete. Asphalt Asphalt [Member] Asphalt. Paving and related services Paving And Related Services [Member] Paving and related services. Other Other Products Or Services [Member] Other products or services. Revenue from External Customer [Line Items] Revenue from External Customer [Line Items] Stockholders' Equity Stockholders' Equity Note Disclosure [Text Block] Members' Interest Members' Equity Notes Disclosure [Text Block] Fair Value Fair Value Disclosures [Text Block] Revenue Recognition Loans, Notes, Trade and Other Receivables Disclosure [Text Block] Statement of Comprehensive Income [Abstract] Comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract] Other comprehensive income (loss): Other Comprehensive Income (Loss), Net of Tax [Abstract] Foreign currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax Income (loss) on cash flow hedges Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification, before Tax Less tax effect of other comprehensive income (loss) items Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent Other comprehensive (loss) income Comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Less comprehensive income attributable to Summit Holdings Comprehensive (Income) Loss, Net of Tax, Attributable to Noncontrolling Interest, Excluding Portion Attributable To Noncontrolling Interest Of Wholly Owned Indirect Subsidiary Of Registrant Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income (loss) and other comprehensive income (loss), attributable to noncontrolling interests, excluding portion attributable to noncontrolling interest of the wholly owned indirect subsidiary of the registrant. Comprehensive income attributable to Summit Inc. Guarantor and Non-Guarantor Financial Information Condensed Financial Statements [Text Block] Schedule of Goodwill [Table] Schedule of Goodwill [Table] Goodwill Goodwill [Line Items] Goodwill [Roll Forward] Goodwill [Roll Forward] Balance, December 29, 2018 Acquisitions Goodwill, Acquired During Period Foreign currency translation adjustments Goodwill, Foreign Currency Translation Gain (Loss) Balance, September 28, 2019 Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Cement plant Cement Plant [Member] Cement plant facility. Number of plants Number of Plants Owned and Operated Number of plants owned and operated by the entity. Voting power (as a percent) Subsidiary Entity Parent Voting Control Percentage The percentage of the the subsidiary's voting power that is controlled by the parent registrant. Revenue by Product Disaggregation of Revenue [Table Text Block] Schedule of Contract Asset and Liability Contract with Customer, Asset and Liability [Table Text Block] Summary of Accounts Receivable, Net Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Movement in Contract Assets and Contract Liabilities [Rollforward] Movement in Contract Assets and Contract Liabilities [Roll Forward] Movement in Contract Assets and Contract Liabilities Change in Contract with Customer, Asset [Abstract] Change in Contract with Customer, Asset [Abstract] Beginning balance Changes in revenue billed, contract price or cost estimates Other Contract with Customer, Asset, Increase (Decrease) for Other Activity Amount of increase (decrease) in right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time, from other activities. Ending balance Change in Contract with Customer, Liability [Abstract] Change in Contract with Customer, Liability [Abstract] Beginning balance Changes in revenue billed, contract price or cost estimates Other Contract with Customer, Liability, Increase (Decrease) for Other Activities Amount of increase (decrease) in obligation to transfer good or service to customer for which consideration from customer has been received or is due, from other activities. Ending balance Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Site Restoration Obligations Site Restoration Obligations [Member] Information pertaining to site restoration obligations arising from regulatory and contractual requirements to perform reclamation activities at the time certain quarries and landfills are closed. Other noncurrent liabilities Other Noncurrent Liabilities [Member] Site restoration obligation, non-current Asset Retirement Obligations, Noncurrent Asset retirement obligation, current Asset Retirement Obligation, Current Anticipated costs Asset Retirement Obligation, Expected Cost Total undiscounted anticipated costs for asset retirement obligations. Term of purchase commitments Purchase Commitment Terms Term of purchase commitment, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Condensed Consolidating Balance Sheets Condensed Balance Sheet [Table Text Block] Condensed Consolidating Statements of Operations and Comprehensive Loss Condensed Income Statement [Table Text Block] Condensed Consolidating Statements of Cash Flows Condensed Cash Flow Statement [Table Text Block]