Name:	sm_DiscountRateUsedForFairValueOfOilAndGasProperties
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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Represents the percentage used to calculate the estimated present value of expected future payment of liability related to deferred compensation plan that have reached payout.

No definition available.

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

Name:	sm_NetProfitsSharingPlanAbstract
Namespace Prefix:	sm_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Name:	sm_OilAndGasPropertiesAbstract
Namespace Prefix:	sm_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Change in commodity prices expressed in percent for sensitivity analysis.

No definition available.

Name:	sm_PercentChangeInCommodityPricesForSensitivityAnalysis
Namespace Prefix:	sm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Change in the discount rate expressed in percentage for sensitivity analysis.

No definition available.

Name:	sm_PercentChangeInDiscountRateForSensitivityAnalysis
Namespace Prefix:	sm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the period of New York Mercantile Exchange (NYMEX) strip pricing used for price forecast.

No definition available.

Name:	sm_PeriodOfNewYorkMercantileExchangeStripPricingUsedForPriceForecast
Namespace Prefix:	sm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Represents the period used for price assumptions of strip prices of liabilities.

No definition available.

Name:	sm_PeriodUsedForPriceAssumptionsOfStripPricesOfLiabilities
Namespace Prefix:	sm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Change in the financial asset or liability resulting from sensitivity analysis due to change in commodity prices.

No definition available.

Name:	sm_SensitivityAnalysisChangeInLiabilityDueToChangeInCommodityPrices
Namespace Prefix:	sm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Change in the financial asset or liability resulting from sensitivity analysis due to decrease in the discount rate.

No definition available.

Name:	sm_SensitivityAnalysisDecreaseInLiabilityDueToChangeInDiscountRate
Namespace Prefix:	sm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

Amount of gain (loss) recognized on the income statement for financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of settlements of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount of transfers of financial instrument classified as a liability into (out of) level 3 of the fair value hierarchy.

No definition available.

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

No definition available.