Document and Entity Information	9 Months Ended
Sep. 30, 2018 shares
Document And Entity Information [Abstract]
Entity Registrant Name	Murphy USA Inc.
Trading Symbol	MUSA
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Entity Central Index Key	0001573516
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Entity Common Stock, Shares Outstanding	32,241,009

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End date of current fiscal year in the format --MM-DD.

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This is focus fiscal period of the document report. For a first quarter 2006 quarterly report, which may also provide financial information from prior periods, the first fiscal quarter should be given as the fiscal period focus. Values: FY, Q1, Q2, Q3, Q4, H1, H2, M9, T1, T2, T3, M8, CY.

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This is focus fiscal year of the document report in CCYY format. For a 2006 annual report, which may also provide financial information from prior periods, fiscal 2006 should be given as the fiscal year focus. Example: 2006.

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The end date of the period reflected on the cover page if a periodic report. For all other reports and registration statements containing historical data, it is the date up through which that historical data is presented. If there is no historical data in the report, use the filing date. The format of the date is CCYY-MM-DD.

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The type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word 'Other'.

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A unique 10-digit SEC-issued value to identify entities that have filed disclosures with the SEC. It is commonly abbreviated as CIK.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Regulation 12B
-Number 240
-Section 12
-Subsection b-2

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The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC.

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Trading symbol of an instrument as listed on an exchange.

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Document And Entity Information [Abstract]

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