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Description of Business and Basis of Presentation (Details) | Aug. 31, 2013 | Aug. 30, 2013 | Dec. 31, 2020 stores states
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Organization, Consolidation and Presentation of Financial Statements [Abstract] |  |  |
Percentage of shares of stock distributed |  | 100.00% |
Ownership interest after transaction (percent) | 0.00% |  |
Number of states in which entity operates | states |  |  | 25
Number of stores | stores |  |  | 1,503

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- Definition Percentage Of Shares Of Stock Distributed + References No definition available. + Details
Name: | musa_PercentageOfSharesOfStockDistributed
Namespace Prefix: | musa_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of states the entity operates in as of the balance sheet date. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
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- Definition Represents the number of stores. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- References No definition available. + Details
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- Definition Percentage of subsidiary's or equity investee's stock owned by parent company after stock transaction. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
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