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Incentive Plans (Narrative) (Details) |  | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Aug. 30, 2013 USD ($) shares | Feb. 28, 2023 peer_company $ / shares | Sep. 30, 2023 USD ($) $ / shares shares | Mar. 31, 2023 USD ($) shares | Sep. 30, 2023 USD ($) $ / shares shares | Sep. 30, 2022 USD ($) | May 04, 2023 shares | Dec. 31, 2022 $ / shares shares | Aug. 08, 2013 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Share-based compensation | $ |  |  |  |  | $ 15,800,000 | $ 11,700,000 |  |  |
Total income tax benefits realized from tax deductions related to stock option exercises under share-based payment arrangements | $ |  |  |  |  | $ 400,000 | $ 1,100,000 |  |  |
MUSA 2013 Plan |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Number of shares authorized for incentive plan (no more than) (in shares) | 5,500,000 |  |  |  |  |  |  |  |
Number of shares per employee (no more than) (in shares) | 1,000,000 |  |  |  |  |  |  |  |
Award expiration period (in years) |  |  |  |  | 7 years |  |  |  |
Shares granted, fair value (in dollars per share) | $ / shares |  | $ 88.53 |  |  |  |  |  |  |
MUSA 2013 Plan | PSUs |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Maximum amount payable | $ | $ 5,000,000 |  |  |  |  |  |  |  |
MUSA 2013 Plan | PSUs | Employees |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Restricted stock units issued, weighted average grant date fair value (in dollars per share) | $ / shares |  |  |  |  | $ 292.52 |  |  |  |
Granted (in shares) |  |  |  |  | 62,275 |  |  |  |
Vested (in shares) |  |  |  |  | 72,799 |  |  |  |
Outstanding (in shares) |  |  | 95,477 |  | 95,477 |  |  | 106,001 |
Weighted average grant date fair value (in dollars per share) | $ / shares |  |  | $ 218.97 |  | $ 218.97 |  |  | $ 160.03 |
MUSA 2013 Plan | PSUs | ROACE |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Award vesting period (in years) |  | 3 years |  |  |  |  |  |  |
Restricted stock units issued, weighted average grant date fair value (in dollars per share) | $ / shares |  | $ 263.48 |  |  |  |  |  |  |
MUSA 2013 Plan | PSUs | TSR |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Award vesting period (in years) |  | 3 years |  |  |  |  |  |  |
Number of companies in total shareholder return peer comparison group | peer_company |  | 17 |  |  |  |  |  |  |
Restricted stock units issued, weighted average grant date fair value (in dollars per share) | $ / shares |  | $ 330.18 |  |  |  |  |  |  |
MUSA 2013 Plan | RSUs | Employees |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Award vesting period (in years) |  |  |  |  | 3 years |  |  |  |
Restricted stock units issued, weighted average grant date fair value (in dollars per share) | $ / shares |  |  |  |  | $ 256.84 |  |  |  |
Granted (in shares) |  |  |  |  | 34,600 |  |  |  |
Vested (in shares) |  |  |  |  | 60,735 |  |  |  |
Outstanding (in shares) |  |  | 120,589 |  | 120,589 |  |  | 149,366 |
Weighted average grant date fair value (in dollars per share) | $ / shares |  |  | $ 198.08 |  | $ 198.08 |  |  | $ 125.51 |
2013 Directors Plan | Non-employee directors |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Number of shares authorized for incentive plan (no more than) (in shares) |  |  |  |  |  |  |  |  | 500,000
2013 Directors Plan | RSUs | Non-employee directors |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Award vesting period (in years) |  |  |  |  | 1 year |  |  |  |
Restricted stock units issued, weighted average grant date fair value (in dollars per share) | $ / shares |  |  |  |  | $ 258.35 |  |  |  |
Granted (in shares) |  |  |  |  | 6,584 |  |  |  |
Vested (in shares) |  |  |  |  | 9,880 |  |  |  |
Outstanding (in shares) |  |  | 23,627 |  | 23,627 |  |  | 26,923 |
Weighted average grant date fair value (in dollars per share) | $ / shares |  |  | $ 177.98 |  | $ 177.98 |  |  | $ 132.38 |
2013 Directors Plan | RSUs | Prior to 2023 | Non-employee directors |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Award vesting period (in years) |  |  |  |  | 3 years |  |  |  |
2013 Directors Plan | RSUs | In 2023 | Non-employee directors |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Award vesting period (in years) |  |  |  |  | 1 year |  |  |  |
2013 Directors Plan | DSUs | Non-employee directors |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Share of common stock right |  |  | 1 |  | 1 |  |  |  |
Granted (in shares) |  |  | 1 | 421 |  |  |  |  |
Vested (in shares) |  |  | 1 |  |  |  |  |  |
Share-based compensation | $ |  |  |  | $ 100,000 |  |  |  |  |
Outstanding (in shares) |  |  | 422 |  | 422 |  |  |  |
Weighted average grant date fair value (in dollars per share) | $ / shares |  |  | $ 258.05 |  | $ 258.05 |  |  |  |
MUSA 2023 Plan |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Number of shares authorized for incentive plan (no more than) (in shares) |  |  |  |  |  |  | 1,725,000 |  |
MUSA 2023 Plan | DSUs | Non-employee directors |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |
Share of common stock right |  |  | 1 |  | 1 |  |  |  |
Granted (in shares) |  |  | 692 |  |  |  |  |  |
Share-based compensation | $ |  |  | $ 200,000 |  |  |  |  |  |
Outstanding (in shares) |  |  | 692 |  | 692 |  |  |  |
Weighted average grant date fair value (in dollars per share) | $ / shares |  |  | $ 325.32 |  | $ 325.32 |  |  |  |

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