Credit Facility and Derivative Counterparties (Details)	Jun. 30, 2021
Derivative Instruments Not Designated as Hedging Instruments [Abstract]
Percentage of proved property secured for credit facility borrowing	85.00%

Percentage of Proved Property Secured for Credit Facility Borrowing

No definition available.

Name:	sm_PercentageofProvedPropertySecuredforCreditFacilityBorrowing
Namespace Prefix:	sm_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant