Incentive Plans	9 Months Ended
Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Incentive Plans	Incentive Plans 2013 Long-Term Incentive Plan Effective August 30, 2013, certain of our employees participate in the Murphy USA 2013 Long-Term Incentive Plan which was subsequently amended and restated effective as of February 8, 2017 (the “MUSA 2013 Plan”). The MUSA 2013 Plan authorizes the Executive Compensation Committee of our Board of Directors (“the Committee”) to grant non-qualified or incentive stock options, stock appreciation rights, stock awards (including restricted stock and restricted stock unit awards), cash awards, and performance awards to our employees. No more than 5.5 million shares of MUSA common stock may be delivered under the MUSA 2013 Plan and no more than 1 million shares of common stock may be awarded to any one employee, subject to adjustment for changes in capitalization. The maximum cash amount payable pursuant to any “performance-based” award to any participant in any calendar year is $5 million. On February 7, 2018, the Committee granted nonqualified stock options for 93,600 shares at an exercise price of $71.00 per share under the terms of the MUSA 2013 Plan. The Black-Scholes valuation for these awards is $17.32 per option. The Committee also awarded time-based restricted stock units and performance-based restricted stock units (performance units) to certain employees on the same date. There were 22,350 time-based restricted units granted at a grant date fair value of $71.00 along with 44,700 performance units. Half of the performance units vest based on a 3-year return on average capital employed (ROACE) calculation and the other half vest based on a 3-year total shareholder return (TSR) calculation that compares MUSA to a group of 16 peer companies. The portion of the awards that vest based on TSR qualify as a market condition and must be valued using a Monte Carlo valuation model. For the TSR portion of the awards, the fair value was determined to be $87.60 per unit. For the ROACE portion of the awards, the valuation will be based on the grant date fair value of $71.00 per unit and the number of awards will be periodically assessed to determine the probability of vesting. On March 27, 2018, the Committee also granted 43,905 time-based restricted stock units granted to certain employees with a grant date fair value of $72.88 per unit. 2013 Stock Plan for Non-employee Directors Effective August 8, 2013, Murphy USA adopted the 2013 Murphy USA Stock Plan for Non-employee Directors (the “Directors Plan”). The directors for Murphy USA are compensated with a mixture of cash payments and equity-based awards. Awards under the Directors Plan may be in the form of restricted stock, restricted stock units, stock options, or a combination thereof. An aggregate of 500,000 shares of common stock shall be available for issuance of grants under the Directors Plan. During the first quarter of 2018, the Company issued 10,800 restricted stock units to its non-employee directors at a grant date fair value of $69.42 per share. These shares vest in three years from the grant date. For the nine months ended September 30, 2018 and 2017, share-based compensation was $6.8 million and $4.7 million, respectively. The income tax benefit realized for the tax deductions from options exercised for the nine months ended September 30, 2018 and 2017 was $2.1 million and $0.2 million, respectively.

Incentive Plans

2013 Long-Term Incentive Plan

Effective August 30, 2013, certain of our employees participate in the Murphy USA 2013 Long-Term Incentive Plan which was subsequently amended and restated effective as of February 8, 2017 (the “MUSA 2013 Plan”). The MUSA 2013 Plan authorizes the Executive Compensation Committee of our Board of Directors (“the Committee”) to grant non-qualified or incentive stock options, stock appreciation rights, stock awards (including restricted stock and restricted stock unit awards), cash awards, and performance awards to our employees. No more than 5.5 million shares of MUSA common stock may be delivered under the MUSA 2013 Plan and no more than 1 million shares of common stock may be awarded to any one employee, subject to adjustment for changes in capitalization. The maximum cash amount payable pursuant to any “performance-based” award to any participant in any calendar year is $5 million.

On February 7, 2018, the Committee granted nonqualified stock options for 93,600 shares at an exercise price of $71.00 per share under the terms of the MUSA 2013 Plan. The Black-Scholes valuation for these awards is $17.32 per option. The Committee also awarded time-based restricted stock units and performance-based restricted stock units (performance units) to certain employees on the same date. There were 22,350 time-based restricted units granted at a grant date fair value of $71.00 along with 44,700 performance units. Half of the performance units vest based on a 3-year return on average capital employed (ROACE) calculation and the other half vest based on a 3-year total shareholder return (TSR) calculation that compares MUSA to a group of 16 peer companies. The portion of the awards that vest based on TSR qualify as a market condition and must be valued using a Monte Carlo valuation model. For the TSR portion of the awards, the fair value was determined to be $87.60 per unit. For the ROACE portion of the awards, the valuation will be based on the grant date fair value of $71.00 per unit and the number of awards will be periodically assessed to determine the probability of vesting.

On March 27, 2018, the Committee also granted 43,905 time-based restricted stock units granted to certain employees with a grant date fair value of $72.88 per unit.

2013 Stock Plan for Non-employee Directors

Effective August 8, 2013, Murphy USA adopted the 2013 Murphy USA Stock Plan for Non-employee Directors (the “Directors Plan”). The directors for Murphy USA are compensated with a mixture of cash payments and equity-based awards. Awards under the Directors Plan may be in the form of restricted stock, restricted stock units, stock options, or a combination thereof. An aggregate of 500,000 shares of common stock shall be available for issuance of grants under the Directors Plan.

During the first quarter of 2018, the Company issued 10,800 restricted stock units to its non-employee directors at a grant date fair value of $69.42 per share. These shares vest in three years from the grant date.

For the nine months ended September 30, 2018 and 2017, share-based compensation was $6.8 million and $4.7 million, respectively. The income tax benefit realized for the tax deductions from options exercised for the nine months ended September 30, 2018 and 2017 was $2.1 million and $0.2 million, respectively.