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v2.4.1.9

Derivative Financial Instruments Credit Facility and Derivative Counterparties (Details) (Line of Credit [Member]) | Dec. 31, 2014
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Line of Credit [Member] |
Line of Credit Facility [Line Items] |
Percentage of Proved Oil and Gas Properties Secured for Credit Facility Borrowing | 75.00%sm_PercentageofProvedOilandGasPropertiesSecuredforCreditFacilityBorrowing / us-gaap_DebtInstrumentAxis = us-gaap_LineOfCreditMember

X
- Definition Percentage of Proved Oil and Gas Properties Secured for Credit Facility Borrowing + References No definition available. + Details
Name: | sm_PercentageofProvedOilandGasPropertiesSecuredforCreditFacilityBorrowing
Namespace Prefix: | sm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_LineOfCreditFacilityLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration