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Derivative Financial Instruments Credit Facility (Details)	Dec. 31, 2020
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Percentage of Proved Property Secured for Credit Facility Borrowing	85.00%

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- Definition

Percentage of Proved Property Secured for Credit Facility Borrowing

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No definition available.

+ Details

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Namespace Prefix:	sm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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- References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration