Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2017
Basis of Presentation	Basis of Presentation The Consolidated Financial Statements include the accounts of Star Group, L.P. and its subsidiaries. All material intercompany items and transactions have been eliminated in consolidation.
Comprehensive Income	Comprehensive Income Comprehensive income is comprised of net income and other comprehensive income. Other comprehensive income consists of the unrealized gain amortization on the Company’s pension plan obligation for its two frozen defined benefit pension plans, and the corresponding tax effect.
Use of Estimates	Use of Estimates The preparation of financial statements in accordance with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from those estimates.
Revenue Recognition	Revenue Recognition Sales of petroleum products are recognized at the time of delivery to the customer and sales of heating and air conditioning equipment are recognized upon completion of installation. Revenue from repairs, maintenance and other services are recognized upon completion of the service. Payments received from customers for equipment service contracts are deferred and amortized into income over the terms of the respective service contracts, on a straight-line basis, which generally do not exceed one year. To the extent that the Company anticipates that future costs for fulfilling its contractual obligations under its service maintenance contracts will exceed the amount of deferred revenue currently attributable to these contracts, the Company recognizes a loss in current period earnings equal to the amount that anticipated future costs exceed related deferred revenues.
Cost of Product	Cost of Product Cost of product includes the cost of home heating oil, diesel, propane, kerosene, heavy oil, gasoline, throughput costs, barging costs, option costs, and realized gains/losses on closed derivative positions for product sales.
Cost of Installations and Services	Cost of Installations and Services Cost of installations and services includes equipment and material costs, wages and benefits for equipment technicians, dispatchers and other support personnel, subcontractor expenses, commissions and vehicle related costs.
Delivery and Branch Expenses	Delivery and Branch Expenses Delivery and branch expenses include wages and benefits and department related costs for drivers, dispatchers, garage mechanics, customer service, sales and marketing, compliance, credit and branch accounting, information technology, vehicle and property rental costs, insurance, weather hedge contract costs and recoveries, and operational management and support.
General and Administrative Expenses	General and Administrative Expenses General and administrative expenses include property rental costs, wages and benefits and department related costs for human resources, finance and corporate accounting, internal audit, administrative support and supply.
Allocation of Net Income	Allocation of Net Income Net income for partners’ capital and statement of operations is allocated to the general partner and the limited partners in accordance with their respective ownership percentages, after giving effect to cash distributions paid to the general partner in excess of its ownership interest, if any.
Net Income per Limited Partner Unit	Net Income per Limited Partner Unit Income per limited partner unit is computed in accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 260-10-05 Earnings Per Share, Master Limited Partnerships (EITF 03-06), by dividing the limited partners’ interest in net income by the weighted average number of limited partner units outstanding. The pro forma nature of the allocation required by this standard provides that in any accounting period where the Company’s aggregate net income exceeds its aggregate distribution for such period, the Company is required to present net income per limited partner unit as if all of the earnings for the periods were distributed, regardless of whether those earnings would actually be distributed during a particular period from an economic or practical perspective. This allocation does not impact the Company’s overall net income or other financial results. However, for periods in which the Company’s aggregate net income exceeds its aggregate distributions for such period, it will have the impact of reducing the earnings per limited partner unit, as the calculation according to this standard results in a theoretical increased allocation of undistributed earnings to the general partner. In accounting periods where aggregate net income does not exceed aggregate distributions for such period, this standard does not have any impact on the Company’s net income per limited partner unit calculation. A separate and independent calculation for each quarter and year-to-date period is performed, in which the Company’s contractual participation rights are taken into account.
Cash Equivalents, Receivables, Revolving Credit Facility Borrowings, and Accounts Payable	Cash Equivalents, Receivables, Revolving Credit Facility Borrowings, and Accounts Payable The carrying amount of cash equivalents, receivables, revolving credit facility borrowings, and accounts payable approximates fair value because of the short maturity of these instruments.
Cash, Cash Equivalents, and Restricted Cash	Cash, Cash Equivalents, and Restricted Cash The Company considers all highly liquid investments with an original maturity of three months or less, when purchased, to be cash equivalents. At September 30, 2017, the $52.7 million of cash, cash equivalents, and restricted cash on the condensed consolidated statement of cash flows is composed of $52.5 million of cash and cash equivalents and $0.3 million of restricted cash. Restricted cash represents deposits held by our captive insurance company that are required by state insurance regulations to remain in the captive insurance company as cash.
Receivables and Allowance for Doubtful Accounts	Receivables and Allowance for Doubtful Accounts Accounts receivables from customers are recorded at the invoiced amounts. Finance charges may be applied to trade receivables that are more than 30 days past due, and are recorded as finance charge income. The allowance for doubtful accounts is the Company’s best estimate of the amount of trade receivables that may not be collectible. The allowance is determined at an aggregate level by grouping accounts based on certain account criteria and its receivable aging. The allowance is based on both quantitative and qualitative factors, including historical loss experience, historical collection patterns, overdue status, aging trends, and current economic conditions. The Company has an established process to periodically review current and past due trade receivable balances to determine the adequacy of the allowance. No single statistic or measurement determines the adequacy of the allowance. The total allowance reflects management’s estimate of losses inherent in its trade receivables at the balance sheet date. Different assumptions or changes in economic conditions could result in material changes to the allowance for doubtful accounts.
Inventories	Inventories Liquid product inventories are stated at the lower of cost or market using the weighted average cost method of accounting. All other inventories, representing parts and equipment are stated at the lower of cost or market using the FIFO method.
Property and Equipment	Property and Equipment Property and equipment are stated at cost. Depreciation is computed over the estimated useful lives of the depreciable assets using the straight-line method over three to thirty years.
Investments	Investments The investments are held by our captive insurance company in an irrevocable trust as collateral for workers’ compensation and automobile liability claims incurred and expected to be incurred in fiscal 2017. The collateral is required by a third party insurance carrier that insures per claim amounts above a set deductible. Due to the expected timing of claim payments, the nature of the collateral agreement with the carrier, and our captive insurance company’s source of other operating cash, the collateral is not expected to be used to pay obligations within the next twelve months. Investments are currently comprised of $11.3 million of Level 1 debt securities measured at fair value and $0.5 million of mutual funds measured at net asset value. See Note 19 – Subsequent Events for discussion of investment activity after September 30, 2017.
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill and intangible assets include goodwill, customer lists, trade names and covenants not to compete. Goodwill is the excess of cost over the fair value of net assets in the acquisition of a company. In accordance with FASB ASC 350-10-05 Intangibles-Goodwill and Other, goodwill and intangible assets with indefinite useful lives are not amortized, but instead are annually tested for impairment. Also in accordance with this standard, intangible assets with finite useful lives are amortized over their respective estimated useful lives to their estimated residual values, and reviewed for impairment. The Company performs its annual impairment review during its fiscal fourth quarter or more frequently if events or circumstances indicate that the value of goodwill might be impaired. Customer lists are the names and addresses of an acquired company’s customers. Based on historical retention experience, these lists are amortized on a straight-line basis over seven to ten years. Trade names are the names of acquired companies. Based on the economic benefit expected and historical retention experience of customers, trade names are amortized on a straight-line basis over seven to twenty years.
Business Combinations	Business Combinations We use the acquisition method of accounting in accordance with FASB ASC 805 Business Combinations. The acquisition method of accounting requires us to use significant estimates and assumptions, including fair value estimates, as of the business combination date, and to refine those estimates as necessary during the measurement period (defined as the period, not to exceed one year, in which the amounts recognized for a business combination may be adjusted). Each acquired company’s operating results are included in our consolidated financial statements starting on the date of acquisition. The purchase price is equivalent to the fair value of consideration transferred. Tangible and identifiable intangible assets acquired and liabilities assumed as of the date of acquisition are recorded at the acquisition date fair value. The separately identifiable intangible assets generally are comprised of customer lists, trade names and covenants not to compete. Goodwill is recognized for the excess of the purchase price over the net fair value of assets acquired and liabilities assumed. Costs that are incurred to complete the business combination such as legal and other professional fees are not considered part of consideration transferred, and are charged to general and administrative expense as they are incurred. For any given acquisition, certain contingent consideration may be identified. Estimates of the fair value of liability or asset classified contingent consideration are included under the acquisition method as part of the assets acquired or liabilities assumed. At each reporting date, these estimates are remeasured to fair value, with changes recognized in earnings.
Impairment of Long-lived Assets	Impairment of Long-lived Assets The Company reviews intangible assets and other long-lived assets in accordance with FASB ASC 360-10-05-4 Property Plant and Equipment, Impairment or Disposal of Long-Lived Assets subsection, for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. The Company determines whether the carrying values of such assets are recoverable over their remaining estimated lives through undiscounted future cash flow analysis. If such a review should indicate that the carrying amount of the assets is not recoverable, the Company will reduce the carrying amount of such assets to fair value.
Deferred Charges	Deferred Charges Deferred charges represent the costs associated with the issuance of the revolving credit facility and are amortized over the life of the facility.
Advertising and Direct Mail Expenses	Advertising and Direct Mail Expenses Advertising and direct mail costs are expensed as they are incurred. Advertising and direct mail expenses were $15.1 million, $14.9 million, and $14.5 million, in 2017, 2016, and 2015, respectively and are recorded in delivery and branch expenses.
Customer Credit Balances	Customer Credit Balances Customer credit balances represent payments received in advance from customers pursuant to a balanced payment plan (whereby customers pay on a fixed monthly basis) and the payments made have exceeded the charges for liquid product and other services.
Environmental Costs	Environmental Costs Costs associated with managing hazardous substances and pollution are expensed on a current basis. Accruals are made for costs associated with the remediation of environmental pollution when it becomes probable that a liability has been incurred and the amount can be reasonably estimated.
Insurance Reserves	Insurance Reserves The Company uses a combination of insurance, self-insured retention and self-insurance for a number of risks, including workers’ compensation, general liability, vehicle liability, medical liability and property. Reserves are established and periodically evaluated, based upon expectations as to what our ultimate liability may be for outstanding claims using developmental factors based upon historical claim experience, including frequency, severity, demographic factors and other actuarial assumptions, supplemented with support from qualified actuaries.
Income Taxes	Income Taxes Prior to November 1, 2017, Star was a master limited partnership and was not subject to tax at the entity level for Federal and State income tax purposes. While Star generated non-qualifying master limited partnership revenue through its corporate subsidiaries, distributions from the corporate subsidiaries to Star are generally included in the determination of qualified master limited partnership income. All or a portion of the distributions received by the Company from the corporate subsidiaries could be a dividend or capital gain to the partners. See Note 19-Subsequent Events for discussion of Company’s tax election effective November 1, 2017. The accompanying financial statements are reported on a fiscal year, however, the Company and its Corporate subsidiaries file Federal and State income tax returns on a calendar year. As most of the Company’s income is derived from its corporate subsidiaries, these financial statements reflect significant Federal and State income taxes. For corporate subsidiaries of the Company, a consolidated Federal income tax return is filed. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amount of assets and liabilities and their respective tax bases and operating loss carry-forwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. A valuation allowance is recognized if, based on the weight of available evidence including historical tax losses, it is more likely than not that some or all of deferred tax assets will not be realized.
Sales, Use and Value Added Taxes	Sales, Use and Value Added Taxes Taxes are assessed by various governmental authorities on many different types of transactions. Sales reported for product, installations and services exclude taxes.
Derivatives and Hedging	Derivatives and Hedging FASB ASC 815-10-05 Derivatives and Hedging, requires that derivative instruments be recorded at fair value and included in the consolidated balance sheet as assets or liabilities. The Company has elected not to designate its derivative instruments as hedging instruments under this guidance, and the changes in fair value of the derivative instruments are recognized in our statement of operations.
Weather Hedge Contract	Weather Hedge Contract To partially mitigate the effect of weather on cash flows, the Company has used weather hedge contracts for a number of years. Weather hedge contracts are recorded in accordance with the intrinsic value method defined by the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 815-45-15 Derivatives and Hedging, Weather Derivatives (EITF 99-2). The premium paid is included in the caption prepaid expenses and other current assets in the accompanying balance sheets and amortized over the life of the contract, with the intrinsic value method applied at each interim period. For fiscal years 2015, 2016 and 2017, the Company had weather hedge contracts that cover the five month period from November 1, through March 31, taken as a whole, for each respective fiscal year. The ultimate amount due to the Company (if any) was based on the entire five month accumulated calculation for the hedge period and had a maximum payout of $12.5 million for each respective fiscal year. During the first quarter of fiscal 2016, the Company recorded a credit of $12.5 million under this contract that reduced delivery and branch expenses. This amount was collected in April 2016. No credit was recorded during the fiscal year ended September 30, 2017.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In April 2015, the FASB issued Accounting Standards Update (“ASU”) No. 2015-03, Interest—Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs. The update requires debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of the related debt liability instead of being presented as an asset. The Company retrospectively adopted the ASU effective December 31, 2016. As a result of the adoption, certain prior year balances (September 30, 2016) changed to conform to the current year presentation as follows: deferred charges and other assets, net decreased from $11.9 million to $11.1 million and long-term debt decreased from $76.3 million to $75.4 million. In September 2015, the FASB issued ASU No. 2015-16, Simplifying the Accounting for Measurement-Period Adjustments, which requires an acquiring entity to recognize adjustments to provisional amounts that are identified during the measurement period in the reporting period in which the adjustment amounts are determined. The acquiring entity is required to record, in the same period’s financial statements, the effect on earnings of changes in depreciation, amortization, or other income effects, if any, as a result of the change to the provisional amounts, calculated as if the accounting had been completed at the acquisition date. In addition, the acquiring entity is to present separately on the face of its income statement or disclose in the notes the portion of the amount recorded in current-period earnings by line item that would have been recorded in previous reporting periods as if the adjustment to the provisional amounts had been recognized as of the acquisition date. The Company adopted the ASU effective December 31, 2016. The adoption of ASU No. 2015-16 did not have an impact on the Company’s consolidated financial statements and related disclosures. In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flow (Topic 230): Restricted cash. The update requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The Company adopted the ASU effective December 31, 2016. The adoption of ASU No. 2016-18 did not have a material impact on the Company’s consolidated financial statements and related disclosures.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. The FASB has also issued several updates to ASU 2014-09. This ASU will replace most existing revenue recognition guidance in GAAP when it becomes effective. This new guidance is effective for our annual reporting period beginning in the first quarter of fiscal 2019, with early adoption permitted beginning in the first quarter of fiscal 2018. The standard permits the use of either the retrospective or cumulative effect transition method. The Company is in the process of evaluating the effect that ASU 2014-09 will have on its revenue streams, consolidated financial statements and related disclosures. The Company has not yet selected a transition method, nor does it intend to early adopt. In July 2015, the FASB issued ASU No. 2015-11, Simplifying the Measurement of Inventory. The update changes the measurement principle for inventory from the lower of cost or market to the lower of cost and net realizable value. This new guidance is effective for our annual reporting period beginning in the first quarter of fiscal 2018, with early adoption permitted. The Company does not expect ASU No. 2015-11 to have a material impact on its consolidated financial statements and related disclosures. In February 2016, the FASB issued ASU No. 2016-02, Leases. The update requires all leases with a term greater than twelve months to be recognized on the balance sheet by calculating the discounted present value of such leases and accounting for them through a right-of-use asset and an offsetting lease liability, and the disclosure of key information pertaining to leasing arrangements. This new guidance is effective for our annual reporting period beginning in the first quarter of fiscal 2020, with early adoption permitted. The Company does not intend to early adopt. The Company is continuing to evaluate the effect that ASU No. 2016-02 could have on its consolidated financial statements and related disclosures, but has not yet selected a transition method. The new guidance will materially change how we account for operating leases for office space, trucks and other equipment. Upon adoption, we expect to recognize discounted right-of-use assets and offsetting lease liabilities related to our operating leases of office space, trucks and other equipment. As of September 30, 2017, the undiscounted future minimum lease payments through 2032 for such operating leases are approximately $134.3 million, but what amount of leasing activity is expected between September 30, 2017, and the date of adoption, are currently unknown. For this reason we are unable to estimate the discounted right-of-use assets and lease liabilities as of the date of adoption. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses. The update broadens the information that an entity should consider in developing expected credit loss estimates, eliminates the probable initial recognition threshold, and allows for the immediate recognition of the full amount of expected credit losses. This new guidance is effective for our annual reporting period beginning in the first quarter of fiscal 2021, with early adoption permitted in the first quarter of fiscal 2020. The Company is evaluating the effect that ASU No. 2016-13 will have on its consolidated financial statements and related disclosures, but has not yet determined the timing of adoption. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flow (Topic 230): Classification of Certain Cash Receipts and Cash Payments. The update addresses the issues of debt prepayment or debt extinguishment costs, settlement of zero-coupon debt instruments or other debt instruments with coupon interest rates that are insignificant in relation to the effective interest rate of the borrowing, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate owned life insurance policies, distributions received from equity method investees, beneficial interests in securitization transactions, and separately identifiable cash flows and application of the predominance principle. This new guidance is effective for our annual reporting period beginning in the first quarter of fiscal 2019, with early adoption permitted. The Company has not determined the timing of adoption, but does not expect ASU 2016-15 to have a material impact on its consolidated financial statements and related disclosures. In January 2017, the FASB issued ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the definition of a business. The update clarifies the definition of a business with the objective of adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. This new guidance is effective for our annual reporting period beginning in the first quarter of fiscal 2019, with early adoption permitted. The Company has not determined the timing of adoption, but does not expect ASU 2017-01 to have a material impact on its consolidated financial statements and related disclosures. In January 2017, the FASB issued ASU No. 2017-04, Intangibles – Goodwill and Other (Topic 230): Simplifying the test for goodwill impairment. The update simplifies how an entity is required to test goodwill for impairment. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value, but not exceed the total amount of goodwill allocated to the reporting unit. This new guidance is effective for our annual reporting period beginning in the first quarter of fiscal 2021, with early adoption permitted. The Company has not determined the timing of adoption, but does not expect ASU 2017-04 to have a material impact on its consolidated financial statements and related disclosures.