Document And Entity Information [Abstract] Document And Entity Information [Abstract] Document Information [Table] Document Information [Table] Class of Stock [Axis] Class Of Stock [Domain] Class of Stock [Domain] Common Class A [Member] Common Class A Common Class B [Member] Common Class B Document Information [Line Items] Document Information [Line Items] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Document Type Document Type Document Period End Date Document Period End Date Amendment Flag Amendment Flag Current Fiscal Year End Date Current Fiscal Year End Date Entity Current Reporting Status Entity Current Reporting Status Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Voluntary Filers Entity Public Float Entity Public Float Membership interests percentage. Membership Interests Percentage Membership interests percentage Membership interests description. Membership Interests Description Membership interests description Consolidated Balance Sheets Statement [Table] Statement [Table] Statement [Line Items] Statement [Line Items] Assets [Abstract] Assets Assets, Current [Abstract] Current assets: Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents-end of period Cash and cash equivalents-beginning of period Cash and cash equivalents Accounts Receivable, Net, Current Accounts receivable, net Accounts receivable, net Costs in Excess of Billings, Current Cost and estimated earnings in excess of billings Costs and estimated earnings in excess of billings Inventory, Net Inventories Total Other Assets, Current Other current assets Assets, Current Total current assets Property, Plant and Equipment, Net Property, plant and equipment, net Property, plant and equipment, net Goodwill Ending balance Beginning balance Goodwill Finite-Lived Intangible Assets, Net Intangible assets Total Deferred Tax Assets, Net, Noncurrent Deferred tax assets Other Assets, Noncurrent Other assets Assets Total assets Total assets Liabilities and Equity [Abstract] Liabilities and Stockholders' Equity / Member's Interest Liabilities, Current [Abstract] Current liabilities: Debt, Current Current portion of debt The amount of consideration for a business acquisition due in the current period. Acquisition Related Liabilities Current Current portion of acquisition-related liabilities Accounts Payable, Current Accounts payable Accrued Liabilities, Current Accrued expenses Total Billings in Excess of Cost, Current Billings in excess of costs and estimated earnings Liabilities, Current Total current liabilities 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). Long Term Debt Noncurrent, Net Long-term debt The amount of consideration for a business acquisition that is not due in the next twelve months. Acquisition Related Liabilities Non Current Acquisition-related liabilities Represents the liability due to former holders of LP Units related to the Tax Receivable Agreement. Tax Receivable Agreement Liability Tax receivable agreement liability Other Liabilities, Noncurrent Other noncurrent liabilities Liabilities Total liabilities Total liabilities Commitments and Contingencies. Commitments and contingencies Stockholders' Equity Attributable to Parent [Abstract] Stockholders' equity / Member's interest Common Stock, Value, Issued Common stock Members' Capital Member's equity Additional Paid in Capital, Common Stock Additional paid-in capital Retained Earnings (Accumulated Deficit) Accumulated earnings Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated other comprehensive income (loss) Members' Equity. Member's interest Stockholders' Equity Attributable to Parent Ending balance Beginning balance Stockholders' equity Stockholders' equity attributable to noncontrolling interest of the wholly owned indirect subsidiary of the registrant. Stockholders' Equity Attributable to Noncontrolling Interest Of Wholly Owned Indirect Subsidiary Of Registrant Noncontrolling interest in consolidated subsidiaries 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. Stockholders' Equity Attributable to Noncontrolling Interest, Excluding Portion Attributable To Noncontrolling Interest Of Wholly Owned Indirect Subsidiary Of Registrant Noncontrolling interest in Summit Materials, Inc. Members' Equity Attributable to Noncontrolling Interest Noncontrolling interest Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Ending Balance Beginning Balance Total stockholders' equity Limited Liability Company (LLC) Members' Equity, Including Portion Attributable to Noncontrolling Interest Ending Balance Beginning Balance Total member's interest Total member's interest Liabilities and Equity Total liabilities and stockholders' equity / member's interest Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Less accumulated depreciation, depletion and amortization Property, plant and equipment, accumulated depreciation, depletion and amortization Finite-Lived Intangible Assets, Accumulated Amortization Accumulated Amortization Intangible assets, accumulated amortization Deferred Tax Assets, Valuation Allowance Less valuation allowance on loss carryforwards Valuation allowance Valuation allowance Common Stock, Par or Stated Value Per Share Common stock, par value Common Stock, Shares Authorized Common stock, shares authorized Common Stock, Shares, Issued Ending Balance (in shares) Beginning Balance (in shares) Common stock, shares issued Common Stock, Shares, Outstanding Common stock, shares outstanding Consolidated Statements of Operations Revenue, Net [Abstract] Revenue: Sales Revenue, Goods, Net Product Sales Revenue, Services, Net Service Revenue, Net Net revenue Net revenue Delivery And Subcontract Revenue Delivery And Subcontract Revenue Delivery and subcontract revenue Revenues Revenue Total revenue Total revenue Cost of Goods and Services Sold [Abstract] Cost of revenue (excluding items shown separately below): Cost of Goods Sold Product Cost of Services Service Cost of Goods and Services Sold Net cost of revenue Delivery and subcontract cost. Delivery And Subcontract Cost Delivery and subcontract cost Cost of Revenue Cost of revenue (excluding items shown separately below) Total cost of revenue General and Administrative Expense General and administrative expenses 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. Depreciation Depletion Amortization And Accretion Depreciation, depletion, amortization and accretion Total depreciation, depletion, amortization and accretion Business Combination, Acquisition Related Costs Transaction costs Operating Income (Loss) Operating income (loss) Operating income Interest Expense Interest expense Gain loss on debt financing. Gain Loss On Debt Financing Loss on debt financings Amount of expense recognized for the period related to the tax receivable agreement. Tax Receivable Agreement Expense Tax receivable agreement expense Other Nonoperating Income (Expense) Other (income) expense, net Other expense (income), net Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest (Loss) income from operations before taxes Income Tax Expense (Benefit) Income tax benefit Income tax expense (benefit) Income tax expense (benefit) Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest Income (loss) from continuing operations Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Income from discontinued operations Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net income (loss) Net income Amount of Net Income (Loss) attributable to noncontrolling interest of the wholly owned indirect subsidiary of the registrant. Net Income Loss Attributable To Noncontrolling Interest Of Wholly Owned Indirect Subsidiary Of Registrant Net income (loss) attributable to noncontrolling interest in subsidiaries Amount of Net Income (Loss) attributable to noncontrolling interest, excluding portion attributable to noncontrolling interest of the wholly owned indirect subsidiary of the registrant. Net Income Loss Attributable To Noncontrolling Interest, Excluding Portion Attributable To Noncontrolling Interest Of Wholly Owned Indirect Subsidiary Of Registrant Net income (loss) attributable to Summit Holdings Net Income (Loss) Attributable to Noncontrolling Interest Net income (loss) attributable to noncontrolling interest Net Income (Loss) Available to Common Stockholders, Basic Net income (loss) attributable to Summit Inc. Net income attributable to Summit Materials, Inc. / member of Summit Materials, LLC Net income (loss) attributable to member of Summit Materials, LLC Net Earnings Per Share Income per share of Class A common stock: Earnings Per Share, Basic Basic Basic income (loss) per share Earnings Per Share, Diluted Diluted earnings per share Diluted Weighted Average Number of Shares Outstanding, Diluted [Abstract] Weighted average shares of Class A common stock: Weighted Average Number of Shares Outstanding, Basic Basic Weighted average shares of Class A common stock outstanding Weighted Average Number of Shares Outstanding, Diluted Diluted Weighted average dilutive shares outstanding Consolidated Statements of Comprehensive Operations Other Comprehensive Income (Loss), Net of Tax [Abstract] Other comprehensive income (loss): Other Comprehensive Income (Loss), Finalization of Pension and Other Postretirement Benefit Plan Valuation, before Tax Postretirement curtailment adjustment Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), before Tax Postretirement liability adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax Foreign currency translation adjustment Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax Income (loss) on cash flow hedges Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent Less tax effect of other comprehensive income (loss) items Other Comprehensive Income (Loss), Net of Tax Other comprehensive income (loss) Other comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Comprehensive income (loss) 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 of the wholly owned indirect subsidiary of the registrant. Comprehensive (Income) Loss, Net of Tax, Attributable to Noncontrolling Interest Of Wholly Owned Indirect Subsidiary Of Registrant Less comprehensive income (loss) attributable to the noncontrolling interest in consolidated subsidiaries 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) Loss, Net of Tax, Attributable to Noncontrolling Interest, Excluding Portion Attributable To Noncontrolling Interest Of Wholly Owned Indirect Subsidiary Of Registrant Less comprehensive income (loss) attributable Summit Holdings Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Less comprehensive income (loss) attributable to noncontrolling interest Comprehensive Income (Loss), Net of Tax, Attributable to Parent Comprehensive income (loss) income attributable to member of Summit Materials, LLC Comprehensive income attributable to Summit Materials, Inc. / Summit Materials, LLC Consolidated Statements of Cash Flows Net Cash Provided by (Used in) Operating Activities [Abstract] Cash flow from operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income to net cash used in operating activities: Depreciation depletion amortization and accretion on asset retirement obligation. Depreciation Depletion Amortization And Accretion On Asset Retirement Obligation Depreciation, depletion, amortization and accretion Share-Based Compensation. Share-based compensation expense Deferred Income Taxes and Tax Credits Deferred income tax benefit (expense) Gain (Loss) on Disposition of Assets Net gain on asset disposals Net gain on asset disposals Goodwill, Impairment Loss Goodwill impairment Non-cash loss on debt refinancing. Non Cash Gain Loss On Debt Refinancing Non-cash loss on debt financings Other Noncash Income (Expense) Other Increase (Decrease) in Operating Assets [Abstract] (Increase) decrease in operating assets, net of acquisitions: Increase (Decrease) in Accounts Receivable Accounts receivable, net Increase (Decrease) in Inventories Inventories Increase (Decrease) in Unbilled Receivables Costs and estimated earnings in excess of billings Increase (Decrease) in Other Current Assets Other current assets Increase (Decrease) in Other Noncurrent Assets Other assets Increase (Decrease) in Operating Liabilities [Abstract] Increase (decrease) in operating liabilities, net of acquisitions: Increase (Decrease) in Accounts Payable Accounts payable Increase (Decrease) in Accrued Liabilities Accrued expenses Increase (Decrease) in Billing in Excess of Cost of Earnings Billings in excess of costs and estimated earnings Amount of increase (decrease) in tax receivable agreement liability. Increase (Decrease) in Tax Receivable Agreement Liability Tax receivable agreement liability Increase (Decrease) in Other Operating Liabilities Other liabilities Net Cash Provided by (Used in) Operating Activities Net cash provided by operating activities Net cash provided by operating activities Net Cash Provided by (Used in) Investing Activities [Abstract] Cash flow from investing activities: Payments to Acquire Businesses, Net of Cash Acquired Acquisitions, net of cash acquired Payments to Acquire Property, Plant, and Equipment Purchase of property, plant and equipment Purchases of property, plant and equipment Total capital expenditures Proceeds from Sale of Property, Plant, and Equipment Proceeds from the sale of property, plant and equipment Proceeds from the sale of property, plant, and equipment Payments for (Proceeds from) Other Investing Activities Other Net Cash Provided by (Used in) Investing Activities Net cash used for investing activities Net cash used for investing activities Net Cash Provided by (Used in) Financing Activities [Abstract] Cash flow from financing activities: Proceeds from Issuance of Common Stock Proceeds from sale of common stock, net of underwriting discounts Proceeds from equity offerings Proceeds from Partnership Contribution Capital contributions by member Payments of Stock Issuance Costs Capital issuance costs Proceeds from Issuance of Debt Net proceeds from debt issuance Proceeds from debt issuances Payments of Financing Costs Debt issuance costs Financing costs Repayments of Debt Payments on debt Payments on long-term debt Payments to Noncontrolling Interests Purchase of noncontrolling interests Cash consideration Payments of Merger Related Costs, Financing Activities Payments on acquisition-related liabilities Payments of Distributions to Affiliates Distributions from partnership Excess Tax Benefit from Share-based Compensation, Financing Activities Proceeds from stock option exercises Proceeds from (Payments for) Other Financing Activities Other Net Cash Provided by (Used in) Financing Activities Net cash provided by financing activities Effect of Exchange Rate on Cash and Cash Equivalents Impact of cash on foreign currency Cash and Cash Equivalents, Period Increase (Decrease) Net increase (decrease) in cash Net increase (decrease) in cash Consolidated Statements of Changes in Stockholders' Equity / Member's Interest and Redeemable Noncontrolling Interest Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] The partnership interests that were the previous form of the entity's equity until the reorganization into a corporation with an IPO. Partners Interest [Member] Partners' Interest Noncontrolling interest attributable to the 20% minority ownership in Ohio Valley Asphalt, LLC. Noncontrolling Interest In Llc [Member] Noncontrolling Interest in subsidiaries Retained Earnings [Member] Accumulated Earnings/Deficit Accumulated Other Comprehensive Income [Member] Accumulated Other Comprehensive Operations Additional Paid In Capital [Member] Additional Paid-in Capital Noncontrolling interest attributable to the ownership in Summit Materials Holdings, L.P., of which Summit Materials, LLC is a an indirect wholly owned subsidiary. Noncontrolling Interest In Lp [Member] Noncontrolling Interest in Summit Inc. Redeemable noncontrolling interest attributable to the 30% minority ownership in Continental Cement Company L.L.C., which was subsequently purchased by the entity. Redeemable Noncontrolling Interest [Member] Redeemable Noncontrolling Interest Aggregate member's equity of a limited liability company (LLC), including noncontrolling interests but excluding redeemable noncontrolling interests. Members Interest Aggregate [Member] Total Member's Interest Increase (Decrease) in Temporary Equity [Roll Forward] Increase (decrease) in redeemable noncontrolling interest Temporary Equity, Carrying Amount, Including Portion Attributable to Noncontrolling Interests Ending Balance Beginning Balance Temporary Equity, Accretion to Redemption Value, Adjustment Accretion/ redemption value adjustment Temporary Equity, Net Income Net income (loss) Temporary Equity, Elimination as Part of Reorganization Purchase of redeemable noncontrolling interest Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (decrease) in stockholders' equity / members' interest and redeemable noncontrolling interest Redeemable Noncontrolling Interest, Equity, Carrying Amount Ending Balance Beginning Balance Capital contributed to limited liability company (LLC). Contribution To Members Equity Net contributed capital Amount of decrease to equity for accretion of temporary equity to its redemption value. Temporary Equity, Accretion to Redemption Value, Equity Impact Accretion/ redemption value adjustment Stockholders' Equity, Change in Reporting Entity Recording of noncontrolling interest upon reorganization The consolidated profit or loss for the period, net of income taxes, excluding portion attributable to temporary equity. Net Income (Loss), Excluding Portion Attributable to Temporary Equity Net income (loss) Stock Issued During Period, Value, New Issues Issuance of Shares Stock Issued During Period, Shares, New Issues Common stock issued (in shares) Issuance of Shares (in shares) Stock Issued During Period, Value, Conversion of Units LP Unit exchanges Stock Issued During Period, Shares, Conversion of Units LP Unit exchanges (in shares) Exchanges during period Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Share-based compensation Stock Repurchased During Period, Shares Share repurchase (in shares) Stock Issued During Period, Value, Stock Options Exercised Stock Option Exercises