Number Of Companies In Total Shareholder Return Peer Comparison Group

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Share Base Compensation Arrangement By Share Based Payment Awards, Maximum Amount Payable

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of tax benefit from exercise of option under share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The highest quantity of shares an employee can purchase under the plan per period.

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Number of shares authorized for issuance under share-based payment arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Gross number of share options (or share units) granted during the period.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Incentive Plans (Narrative) (Details)	12 Months Ended			76 Months Ended
Incentive Plans (Narrative) (Details)	Dec. 31, 2020 USD ($) $ / shares peerCompanies shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2019 shares	Feb. 12, 2014 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	79,200
Unrecognized compensation cost related to stock option awards \| $	$ 18,100,000
Unrecognized compensation cost related to stock option awards, weighted average period for recognition (in years)	1 year 8 months 12 days
Total income tax benefits realized from tax deductions related to stock option exercises under share-based payment arrangements \| $	$ 700,000	$ 100,000	$ 2,100,000
2013 Long-Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares authorized for incentive plan (in shares)					5,500,000
Maximum number of shares per employee (in shares)	1,000,000
Maximum amount payable \| $	$ 5,000,000.0
Shares granted (in shares)				2,491,559
Shares available for grant (in shares)	3,008,441
2013 Stock Plan For Non-Employee Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares authorized for incentive plan (in shares)	500,000
Shares available for grant (in shares)	366,570
Restricted stock units issued (in shares)				133,430
2013 Stock Plan For Non-Employee Directors \| Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units issued (in shares)	9,801
Award vesting period (in years)	3 years
Restricted stock units issued, weighted average grant date fair value (in dollars per share) \| $ / shares	$ 105.33
MUSA 2013 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units issued (in shares)	55,734
Option term (in years)	7 years
Restricted stock units issued, weighted average grant date fair value (in dollars per share) \| $ / shares	$ 90.09
MUSA 2013 Plan \| Return On Average Capital Employed Performance Units
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	$ 106.72
MUSA 2013 Plan \| Total Shareholder Return Performance Units
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 \| peerCompanies	18
Restricted stock units issued, weighted average grant date fair value (in dollars per share) \| $ / shares	$ 142.07
MUSA 2013 Plan \| Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)	3 years