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

Assumption used in valuing an instrument.

No definition available.

Name:	sm_FairValueAssumptionsMeasurementInput
Namespace Prefix:	sm_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

Impairment of Proved, Unproved, and Other Properties [Abstract]

No definition available.

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

Major Customers [Abstract]

No definition available.

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

Number of individual entities within groups of entities under common ownership that represent more than 10 percent of total production revenue

No definition available.

Name:	sm_Numberofindividualentitieswithingroupsofentitiesundercommonownershipthatrepresentmorethan10percentoftotalproductionrevenue
Namespace Prefix:	sm_
Data Type:	xbrli:integerItemType
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:durationItemType
Balance Type:	na
Period Type:	duration

Revenue Receipt, Days After Sale

No definition available.

Name:	sm_RevenueReceiptDaysAfterSale
Namespace Prefix:	sm_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13531-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13537-108611

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

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

- References

No definition available.

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

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

No definition available.

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

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

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_OilAndGasPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CustomerConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=sm_OilGasandNGLsSalesRevenueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_MajorCustomersAxis=sm_MajorCustomerOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_MajorCustomersAxis=sm_MajorCustomerTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_MajorCustomersAxis=sm_MajorCustomerThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_MajorCustomersAxis=sm_MajorCustomerFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_MajorCustomersAxis=sm_UnnamedMajorCustomerGroupOnewithRelatedEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_MajorCustomersAxis=sm_UnnamedMajorCustomerGroupTwowithRelatedEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_PropertyPlantAndEquipmentOtherTypesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputDiscountRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputRiskFreeInterestRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FairValueByLiabilityClassAxis=us-gaap_AssetRetirementObligationCostsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: