INCOME TAXES	9 Months Ended
INCOME TAXES	Sep. 28, 2019
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Summit Inc.’s tax provision includes its proportional share of Summit Holdings’ tax attributes. Summit Holdings’ subsidiaries are primarily limited liability companies, but do include certain entities organized as C corporations and a Canadian subsidiary. The tax attributes related to the limited liability companies are passed on to Summit Holdings and then to its partners, including Summit Inc. The tax attributes associated with the C corporation and Canadian subsidiaries are fully reflected in the Company’s accounts. Our income tax expense was $45.6 million and $34.3 million in the three and nine months ended September 28, 2019, respectively, and our income tax expense was $20.8 million and $16.2 million in the three and nine months ended September 29, 2018, respectively. The effective tax rate for Summit Inc. differs from the federal rate primarily due to (1) unrecognized tax benefits related in the deductibility of interest expense as noted below, (2) state taxes, (3) tax depletion expense in excess of the expense recorded under U.S. GAAP, (4) the minority interest in the Summit Holdings partnership that is allocated outside of the Company and (5) various other items such as limitations on meals and entertainment, certain stock compensation and other costs. In the three and nine months ended September 28, 2019, the increase in the Company's effective tax rate, and related income tax expense, over the prior year is in response to the adoption of proposed regulations issued in late 2018 related to tax reform legislation. The Company’s income tax provision is calculated under the provisions of the proposed regulations, which will limit our ability to deduct interest expense in calculating our taxable income. Once the final regulations are issued, the Company will adjust its calculations, if necessary. As of September 28, 2019 and December 29, 2018, Summit Inc. had a valuation allowance of $29.5 million and $19.4 million, respectively, which relates to certain deferred tax assets in taxable entities where realization is not more likely than not. Summit Inc. and its subsidiaries expect additional unrecognized tax benefits related to the deductibility of interest expense in 2019 that if recognized would affect the annual effective tax rate, and included that in its estimate of those amounts in its annual effective tax rate. We did not recognize interest or penalties related to this amount as it is offset by other attributes. No material interest or penalties were recognized in income tax expense during the three and nine months ended September 28, 2019 and September 29, 2018. No uncertain tax benefits were recognized in the three and nine months ended September 29, 2018. Tax Receivable Agreement—The Company is party to a TRA with certain current and former holders of LP Units that provides for the payment by Summit Inc. to exchanging holders of LP Units of 85% of the benefits, if any, that Summit Inc. actually realizes (or, under certain circumstances such as an early termination of the TRA, is deemed to realize) as a result of increases in the tax basis of tangible and intangible assets of Summit Holdings and certain other tax benefits related to entering into the TRA, including tax benefits attributable to payments under the TRA. In the nine months ended September 28, 2019, 107,336 LP Units were acquired by Summit Inc. in exchange for an equal number of newly-issued shares of Summit Inc.’s Class A common stock. These exchanges resulted in net new deferred tax assets of approximately $0.4 million. As we determined that the deferred tax assets created from these exchanges are realizable and payment under the TRA is considered probable, we have recorded 85% of the increase in deferred tax assets as TRA liability and the remainder as an increase in additional paid in capital. As of September 28, 2019 and December 29, 2018, we had recorded $310.1 million and $310.3 million of TRA liability, respectively, of which $0.6 million was classified as accrued expenses as of December 29, 2018. Tax Distributions – The holders of Summit Holdings’ LP Units, including Summit Inc., incur U.S. federal, state and local income taxes on their share of any taxable income of Summit Holdings. The limited partnership agreement of Summit Holdings provides for pro rata cash distributions (“tax distributions”) to the holders of the LP Units in an amount generally calculated to provide each holder of LP Units with sufficient cash to cover its tax liability in respect of the LP Units. In general, these tax distributions are computed based on Summit Holdings’ estimated taxable income allocated to Summit Inc. multiplied by an assumed tax rate equal to the highest effective marginal combined U.S. federal, state and local income tax rate in New York, New York. Summit Holdings did not make any tax distributions in the nine months ended September 28, 2019 and made $0.1 million in tax distributions in the nine months ended September 29, 2018.
Summit Materials, LLC
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Summit LLC is a limited liability company and passes its tax attributes for federal and state tax purposes to its parent company and is generally not subject to federal or state income tax. However, certain subsidiary entities file federal, state and Canadian income tax returns due to their status as taxable entities in the respective jurisdiction. The effective income tax rate for the C Corporations differs from the statutory federal rate primarily due to (1) tax depletion expense in excess of the expense recorded under U.S. GAAP, (2) state income taxes and the effect of graduated tax rates and (3) various other items, such as limitations on meals and entertainment and other costs. The effective income tax rate for the Canadian subsidiary is not significantly different from its historical effective tax rate. Summit LLC and its subsidiaries expect additional unrecognized tax benefits related to the deductibility of interest expense in 2019 that if recognized would affect the annual effective tax rate, and included that in its estimate of those amounts in its annual effective tax rate. We did not recognize interest or penalties related to this amount as it is offset by other attributes. No material interest or penalties were recognized in income tax expense during the three and nine months ended September 28, 2019 and September 29, 2018. No uncertain tax benefits were recognized in the three and nine months ended September 29, 2018.