Description of Business and Basis of Presentation (Policies)	6 Months Ended
Jun. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	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.
Recently Issued Accounting Standards	Recently Issued Accounting Standards— In March 2020, the FASB issued ASU 2020-04, "Reference Rate Reform (Topic 848) - Facilitation of the Effects of Reference Rate Reform on Financial Reporting". This standard included optional guidance for a limited period of time to help ease the burden in accounting for the effects of reference rate reform. The new standard is effective for all entities through December 31, 2022. The Company does not expect the adoption of this standard to have a material impact on the Company's consolidated financial statements. 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 was effective for the Company on January 1, 2020. The amendments in this update were applied prospectively to all implementation costs incurred after the date of adoption. The Company assessed the effect that this ASU had on our financial position, results of operations, and disclosures and determined that this update did not have a material impact on the Company's consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, "Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments." ASU 2016-13 was subsequently modified by ASU 2018-19, ASU 2019-04, ASU 2019-05, and ASU 2019-11. This ASU changes the way entities recognize impairment of many financial assets by requiring immediate recognition of estimated credit losses expected to occur over their remaining life, which will result in timelier recognition of losses. ASU 2016-13 and the associated modifications were effective for the Company on January 1, 2020. ASC 326 requires a modified retrospective approach with an adjustment at the beginning of the year for any adjustment due to its adoption. In applying ASC 326 at January 1, 2020, the Company calculated an adjustment to its estimated credit loss allowance and lowered the allowance by $1.1 million, which was credited to retained earnings under the modified retrospective approach. The adjustment reflects the Company's changes in credit practices since its spin-off in 2013 which includes tighter applied credit terms and faster turnover of receivable balances resulting in a decrease to its estimated credit loss allowance as of January 1, 2020. A review was conducted for the quarter ended June 30, 2020, and no change in the estimated credit loss allowance was required.
Revenue Recognition	Revenue Recognition Revenue is recognized when obligations under the terms of a contract with our customers are satisfied; generally, this occurs with the transfer of control of our petroleum products, convenience merchandise, Renewable Identification Numbers ("RINs") and other assets to our third-party customers. Revenue is measured as the amount of consideration we expect to receive in exchange for transferring goods or providing services. Excise and sales tax that we collect where we have determined we are the principal in the transaction have been recorded as revenue on a jurisdiction-by-jurisdiction basis. The Company enters into buy/sell and similar arrangements when petroleum products are held at one location but are needed at a different location. The Company often pays or receives funds related to the buy/sell arrangements based on location or quality differences. The Company continues to account for these transactions as non-monetary exchanges under existing accounting guidance and typically reports these on a net basis in the Consolidated Statements of Income. Petroleum product sales (at retail). For our retail store locations, the revenue related to petroleum product sales is recognized as the fuel is pumped to our customers. The transaction price at the pump typically includes some portion of sales or excise taxes as levied in the respective jurisdictions. Those taxes that are collected for remittance to governmental entities on a pass through basis are not recognized as revenue and they are recorded to a liability account until they are paid. Our customers typically use a mixture of cash, checks, credit cards and debit cards to pay for our products as they are received. We have accounts receivable from the various credit/debit card providers at any point in time related to product sales made on credit cards and debit cards. These receivables are typically collected in two to seven days, depending on the terms with the particular credit/debit card providers. Payment fees retained by the credit/debit card providers are recorded as station and other operating expenses. Petroleum product sales (at wholesale). Our sales of petroleum products at wholesale are generally recorded as revenue when the deliveries have occurred and legal ownership of the product has transferred to the customer. Title transfer for bulk refined product sales typically occurs at pipeline custody points and upon trucks loading at product terminals. For bulk pipeline sales, we record receivables from customers that are generally collected within a week from custody transfer date. For our rack product sales, the majority of our customers' accounts are drafted by us within 10 days from product transfer. Merchandise sales. For our retail store locations, the revenue related to merchandise sales is recognized as the customer completes their purchase at our locations. The transaction price typically includes some portion of sales tax as levied in the respective jurisdictions. Those taxes that are collected for remittance to governmental entities on a pass through basis are not recognized as revenue and they are recorded to a liability account until they are paid. As noted above, a mixture of payment types are used for these revenues and the same terms for credit/debit card receivables are realized. The most significant judgment with respect to merchandise sales revenue is determining whether we are the principal or agent for some categories of merchandise such as lottery tickets, lotto tickets, newspapers and other small categories of merchandise. For scratch-off lottery tickets, we have determined we are the principal in the majority of the jurisdictions and therefore we record those sales on a gross basis. We have some categories of merchandise (such as lotto tickets) where we are the agent and the revenues recorded for those transactions are our net commission only. In June 2018, the Company initiated a loyalty pilot program through a limited number of its retail locations. The customers earn rewards based on their spending or other promotional activities. This program creates a performance obligation which requires us to defer a portion of sales revenue to the loyalty program participants until they redeem their rewards or the rewards expire. The rewards may be redeemed for merchandise or cash discounts on fuel purchases. The program was rolled out chain-wide in March 2019. The deferred revenue balances at June 30, 2020 and December 31, 2019 were immaterial. RINs sales. For the sale of RINs, we recognize revenue when the RIN is transferred to the counter-party and the sale is completed. Receivables from our counter-parties related to the RIN sales are typically collected within five days of the sale. Other revenues. Items reported as other operating revenues include collection allowances for excise and sales tax and other miscellaneous items and are recognized as revenue when the transaction is completed.
Lease Accounting	Leases with an initial term of 12 months or less are not recorded on the balance sheet; we recognize lease expense for these leases on a straight-line basis over the lease term.

Description of Business and Basis of Presentation (Policies)

6 Months Ended

Jun. 30, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

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.

Recently Issued Accounting Standards

Recently Issued Accounting Standards—

In March 2020, the FASB issued ASU 2020-04, "Reference Rate Reform (Topic 848) - Facilitation of the Effects of Reference Rate Reform on Financial Reporting". This standard included optional guidance for a limited period of time to help ease the burden in accounting for the effects of reference rate reform. The new standard is effective for all entities through December 31, 2022. The Company does not expect the adoption of this standard to have a material impact on the Company's consolidated financial statements.

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 was effective for the Company on January 1, 2020. The amendments in this update were applied prospectively to all implementation costs incurred after the date of adoption. The Company assessed the effect that this ASU had on our financial position, results of operations, and disclosures and determined that this update did not have a material impact on the Company's consolidated financial statements.

In June 2016, the FASB issued ASU 2016-13, "Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments." ASU 2016-13 was subsequently modified by ASU 2018-19, ASU 2019-04, ASU 2019-05, and ASU 2019-11. This ASU changes the way entities recognize impairment of many financial assets by requiring immediate recognition of estimated credit losses expected to occur over their remaining life, which will result in timelier recognition of losses. ASU 2016-13 and the associated modifications were effective for the Company on January 1, 2020. ASC 326 requires a modified retrospective approach with an adjustment at the beginning of the year for any adjustment due to its adoption.

In applying ASC 326 at January 1, 2020, the Company calculated an adjustment to its estimated credit loss allowance and lowered the allowance by $1.1 million, which was credited to retained earnings under the modified retrospective approach. The adjustment reflects the Company's changes in credit practices since its spin-off in 2013 which includes tighter applied credit terms and faster turnover of receivable balances resulting in a decrease to its estimated credit loss allowance as of January 1, 2020. A review was conducted for the quarter ended June 30, 2020, and no change in the estimated credit loss allowance was required.

Revenue Recognition

Revenue is recognized when obligations under the terms of a contract with our customers are satisfied; generally, this occurs with the transfer of control of our petroleum products, convenience merchandise, Renewable Identification Numbers ("RINs") and other assets to our third-party customers. Revenue is measured as the amount of consideration we expect to receive in exchange for transferring goods or providing services. Excise and sales tax that we collect where we have determined we are the principal in the transaction have been recorded as revenue on a jurisdiction-by-jurisdiction basis.

The Company enters into buy/sell and similar arrangements when petroleum products are held at one location but are needed at a different location. The Company often pays or receives funds related to the buy/sell arrangements based on location or quality differences. The Company continues to account for these transactions as non-monetary exchanges under existing accounting guidance and typically reports these on a net basis in the Consolidated Statements of Income.

Petroleum product sales (at retail). For our retail store locations, the revenue related to petroleum product sales is recognized as the fuel is pumped to our customers. The transaction price at the pump typically includes some portion of sales or excise taxes as levied in the respective jurisdictions. Those taxes that are collected for remittance to governmental entities on a pass through basis are not recognized as revenue and they are recorded to a liability account until they are paid. Our customers typically use a mixture of cash, checks, credit cards and debit cards to pay for our products as they are received. We have accounts receivable from the various credit/debit card providers at any point in time related to product sales made on credit cards and debit cards. These receivables are typically collected in two to seven days, depending on the terms with the particular credit/debit card providers. Payment fees retained by the credit/debit card providers are recorded as station and other operating expenses.

Petroleum product sales (at wholesale). Our sales of petroleum products at wholesale are generally recorded as revenue when the deliveries have occurred and legal ownership of the product has transferred to the customer. Title transfer for bulk refined product sales typically occurs at pipeline custody points and upon trucks loading at product terminals. For bulk pipeline sales, we record receivables from customers that are generally collected within a week from custody transfer date. For our rack product sales, the majority of our customers' accounts are drafted by us within 10 days from product transfer.

Merchandise sales. For our retail store locations, the revenue related to merchandise sales is recognized as the customer completes their purchase at our locations. The transaction price typically includes some portion of sales tax as levied in the respective jurisdictions. Those taxes that are collected for remittance to governmental entities on a pass through basis are not recognized as revenue and they are recorded to a liability account until they are paid. As noted above, a mixture of payment types are used for these revenues and the same terms for credit/debit card receivables are realized.

The most significant judgment with respect to merchandise sales revenue is determining whether we are the principal or agent for some categories of merchandise such as lottery tickets, lotto tickets, newspapers and other small categories of merchandise. For scratch-off lottery tickets, we have determined we are the principal in the majority of the jurisdictions and therefore we record those sales on a gross basis. We have some categories of merchandise (such as lotto tickets) where we are the agent and the revenues recorded for those transactions are our net commission only.

In June 2018, the Company initiated a loyalty pilot program through a limited number of its retail locations. The customers earn rewards based on their spending or other promotional activities. This program creates a performance obligation which requires us to defer a portion of sales revenue to the loyalty program participants until they redeem their rewards or the rewards expire. The rewards may be redeemed for merchandise or cash discounts on fuel purchases. The program was rolled out chain-wide in March 2019. The deferred revenue balances at June 30, 2020 and December 31, 2019 were immaterial.

RINs sales. For the sale of RINs, we recognize revenue when the RIN is transferred to the counter-party and the sale is completed. Receivables from our counter-parties related to the RIN sales are typically collected within five days of the sale.

Other revenues. Items reported as other operating revenues include collection allowances for excise and sales tax and other miscellaneous items and are recognized as revenue when the transaction is completed.

Lease Accounting

Leases with an initial term of 12 months or less are not recorded on the balance sheet; we recognize lease expense for these leases on a straight-line basis over the lease term.