Description of Business and Basis of Presentation	9 Months Ended
Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business and Basis of Presentation	Description of Business and Basis of Presentation Description of business — Murphy USA Inc. (“Murphy USA” or the “Company”) markets refined products through a network of retail gasoline stations and to unbranded wholesale customers. Murphy USA’s owned retail stations are almost all located in close proximity to Walmart stores in 26 states and use the brand name Murphy USA®. Murphy USA also markets gasoline and other products at standalone stations under the Murphy Express brand. At September 30, 2018, Murphy USA had a total of 1,461 Company stations of which 1,160 were Murphy USA and 301 were Murphy Express. Basis of Presentation — Murphy USA was incorporated in March 2013 and, in connection with its incorporation, Murphy USA issued 100 shares of common stock, par value $0.01 per share, to Murphy Oil Corporation (“Murphy Oil”) for $1.00. On August 30, 2013, Murphy USA was separated from Murphy Oil through the distribution of 100% of the common stock of Murphy USA to holders of Murphy Oil stock. In preparing the financial statements of Murphy USA in conformity with accounting principles generally accepted in the United States, management has made a number of estimates and assumptions related to the reporting of assets, liabilities, revenues, expenses and the disclosure of contingent assets and liabilities. Actual results may differ from these estimates. Interim Financial Information — The interim period financial information presented in these consolidated financial statements is unaudited and includes all known accruals and adjustments, in the opinion of management, necessary for a fair presentation of the consolidated financial position of Murphy USA and its results of operations and cash flows for the periods presented. All such adjustments are of a normal and recurring nature. These interim consolidated financial statements should be read together with our audited financial statements for the years ended December 31, 2017, 2016 and 2015, included in our Annual Report on Form 10-K (File No. 001-35914), as filed with the Securities and Exchange Commission under the Securities Exchange Act of 1934 on February 20, 2018. Recently Issued Accounting Standards— In May 2014, the FASB issued Accounting Standards Update No. 2014-09 (Topic 606) "Revenue from Contracts with Customers". Topic 606 supersedes the revenue recognition requirements Topic 605, "Revenue Recognition" (Topic 605), and requires entities to recognize revenue when control of the promised goods or services is transferred to customers at an amount that reflects the consideration to which the entity expects to be entitled to in exchange for those goods or services. We adopted Topic 606 as of January 1, 2018 using the modified retrospective transition method. See Note 2 "Revenues" for further details. In February 2016, the FASB issued ASU No. 2016-02, "Leases (Topic 842)" (“ASU 2016-02”). ASU 2016-02 amends the existing accounting standards for lease accounting by recognizing lease assets and lease liabilities on the balance sheet for those leases classified as operating leases under current GAAP. ASU 2016-02 requires that a lessee should recognize a liability to make lease payments (the lease liability) and a right-of-use asset representing its right to use the underlying asset for the lease term on the balance asset. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018 (including interim periods within those periods) using a modified retrospective approach and early adoption is permitted. The Company will adopt ASU 2016-02 in the first quarter of 2019 and is in the process of implementing changes to its systems and processes in conjunction with its review of lease agreements. We have implemented a third-party software solution to assist with the accounting under the new standard and are nearing completion of our testing and optimization of the system. The Company is also finalizing procedures to validate the completeness of its inventory of arrangements that meet the new definition of an operating lease, in parallel to documenting internal policy decisions and permitted elections. Although we are in the process of evaluating the impact of adoption of the ASU on our consolidated financial statements, the Company currently believes the most significant change will be related to the recognition of right-of-use assets and lease liabilities on its balance sheet for real estate operating leases. Further, the Company is assessing if there are any embedded leases in arrangements with suppliers and customers that may result in right to use assets. In November 2016, the FASB issued ASU 2016-18, "Statement of Cash Flows (Topic 230): Restricted Cash". This ASU requires that a Statement of Cash Flows explain the change during the period in the total cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Restricted cash and restricted cash equivalents will be included with cash and cash equivalents when reconciling the beginning of period and end of period balances on the Statement of Cash Flows upon adoption of this standard. The standard was effective for the Company on January 1, 2018 and was applied retrospectively to the Statement of Cash Flows. Accordingly, the Consolidated Statement of Cash Flows presents a reconciliation of the changes in cash, cash equivalents and restricted cash. Restricted cash consists of funds held by third party intermediaries for like-kind property exchanges and is reported as a long-term asset in the Company's Balance Sheet. In August 2018, the FASB issued ASU 2018-15, "Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract". This ASU aligns the accounting treatment for capitalizing implementation costs incurred by customers in cloud computing arrangements in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. This guidance is effective for the Company on January 1, 2020. Early adoption is permitted. The amendments in this update should be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. The Company is currently assessing the effect that this ASU will have on our financial position, results of operations, and disclosures but does not expect this update to have a material impact on the Company's consolidated financial statements.

Description of Business and Basis of Presentation

Description of business — Murphy USA Inc. (“Murphy USA” or the “Company”) markets refined products through a network of retail gasoline stations and to unbranded wholesale customers. Murphy USA’s owned retail stations are almost all located in close proximity to Walmart stores in 26 states and use the brand name Murphy USA®. Murphy USA also markets gasoline and other products at standalone stations under the Murphy Express brand. At September 30, 2018, Murphy USA had a total of 1,461 Company stations of which 1,160 were Murphy USA and 301 were Murphy Express.

Basis of Presentation — Murphy USA was incorporated in March 2013 and, in connection with its incorporation, Murphy USA issued 100 shares of common stock, par value $0.01 per share, to Murphy Oil Corporation (“Murphy Oil”) for $1.00. On August 30, 2013, Murphy USA was separated from Murphy Oil through the distribution of 100% of the common stock of Murphy USA to holders of Murphy Oil stock.

In preparing the financial statements of Murphy USA in conformity with accounting principles generally accepted in the United States, management has made a number of estimates and assumptions related to the reporting of assets, liabilities, revenues, expenses and the disclosure of contingent assets and liabilities. Actual results may differ from these estimates.

Interim Financial Information — The interim period financial information presented in these consolidated financial statements is unaudited and includes all known accruals and adjustments, in the opinion of management, necessary for a fair presentation of the consolidated financial position of Murphy USA and its results of operations and cash flows for the periods presented. All such adjustments are of a normal and recurring nature.

These interim consolidated financial statements should be read together with our audited financial statements for the years ended December 31, 2017, 2016 and 2015, included in our Annual Report on Form 10-K (File No. 001-35914), as filed with the Securities and Exchange Commission under the Securities Exchange Act of 1934 on February 20, 2018.

Recently Issued Accounting Standards—

In May 2014, the FASB issued Accounting Standards Update No. 2014-09 (Topic 606) "Revenue from Contracts with Customers". Topic 606 supersedes the revenue recognition requirements Topic 605, "Revenue Recognition" (Topic 605), and requires entities to recognize revenue when control of the promised goods or services is transferred to customers at an amount that reflects the consideration to which the entity expects to be entitled to in exchange for those goods or services. We adopted Topic 606 as of January 1, 2018 using the modified retrospective transition method. See Note 2 "Revenues" for further details.

In February 2016, the FASB issued ASU No. 2016-02, "Leases (Topic 842)" (“ASU 2016-02”). ASU 2016-02 amends the existing accounting standards for lease accounting by recognizing lease assets and lease liabilities on the balance sheet for those leases classified as operating leases under current GAAP. ASU 2016-02 requires that a lessee should recognize a liability to make lease payments (the lease liability) and a right-of-use asset representing its right to use the underlying asset for the lease term on the balance asset. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018 (including interim periods within those periods) using a modified retrospective approach and early adoption is permitted. The Company will adopt ASU 2016-02 in the first quarter of 2019 and is in the process of implementing changes to its systems and processes in conjunction with its review of lease agreements. We have implemented a third-party software solution to assist with the accounting under the new standard and are nearing completion of our testing and optimization of the system. The Company is also finalizing procedures to validate the completeness of its inventory of arrangements that meet the new definition of an operating lease, in parallel to documenting internal policy decisions and permitted elections. Although we are in the process of evaluating the impact of adoption of the ASU on our consolidated financial statements, the Company currently believes the most significant change will be related to the recognition of right-of-use assets and lease liabilities on its balance sheet for real estate operating leases. Further, the Company is assessing if there are any embedded leases in arrangements with suppliers and customers that may result in right to use assets.

In November 2016, the FASB issued ASU 2016-18, "Statement of Cash Flows (Topic 230): Restricted Cash". This ASU requires that a Statement of Cash Flows explain the change during the period in the total cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Restricted cash and restricted cash equivalents will be included with cash and cash equivalents when reconciling the beginning of period and end of period balances on the Statement of Cash Flows upon adoption of this standard. The standard was effective for the Company on January 1, 2018 and was applied retrospectively to the Statement of Cash Flows. Accordingly, the Consolidated Statement of Cash Flows presents a reconciliation of the changes in cash, cash equivalents and restricted cash. Restricted cash consists of funds held by third party intermediaries for like-kind property exchanges and is reported as a long-term asset in the Company's Balance Sheet.

In August 2018, the FASB issued ASU 2018-15, "Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract". This ASU aligns the accounting treatment for capitalizing implementation costs incurred by customers in cloud computing arrangements in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. This guidance is effective for the Company on January 1, 2020. Early adoption is permitted. The amendments in this update should be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. The Company is currently assessing the effect that this ASU will have on our financial position, results of operations, and disclosures but does not expect this update to have a material impact on the Company's consolidated financial statements.