Multiplier Applied to PSU Awards Upon Settlement

No definition available.

Name:	sm_MultiplierAppliedtoPSUAwardsUponSettlement
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- Definition

Number of Shares Represented by Each RSU

+ References

No definition available.

+ Details

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Period over which company performance is measured in order to compute the multiplier to apply to PSU awards

+ References

No definition available.

+ Details

Name:	sm_ShareBasedCompensationAwardsOtherThanOptionsPerformanceMeasurementPeriod
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- Definition

Share-based Compensation Arragement by Share-based Payment Award, Maximum Employee Purchase Amount

+ References

No definition available.

+ Details

Name:	sm_SharebasedCompensationArragementbySharebasedPaymentAwardMaximumEmployeePurchaseAmount
Namespace Prefix:	sm_
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Balance Type:	debit
Period Type:	instant

- Definition

Share-based Compensation Arrangement by Share-Based Payment Award, Percent of Offering Date Price Paid

+ References

No definition available.

+ Details

Name:	sm_SharebasedCompensationArrangementbyShareBasedPaymentAwardPercentofOfferingDatePricePaid
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Balance Type:	na
Period Type:	instant

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Total Fair Value

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Awarded per Performance Stock Unit

+ References

No definition available.

+ Details

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

- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 14.F)

-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section F

+ Details

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

- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The number of restricted shares issued as compensation, net of shares for the payment of withholding taxes. This element is to be used only if shares are used in lieu of cash to satisfy all or a portion of withholding taxes.

+ References

No definition available.

+ Details

Name:	us-gaap_RestrictedStockSharesIssuedNetOfSharesForTaxWithholdings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(iii)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

+ References

No definition available.

+ Details

Name:	us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Gross number of shares (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP). Shares issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans.

+ References

No definition available.

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_PerformanceSharesMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
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- Details

Name:	us-gaap_AwardTypeAxis=sm_SharesIssuedtotheBoardofDirectorsMember
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- Details

Name:	us-gaap_AwardTypeAxis=sm_SharesIssuedtotheBoardofDirectorsDirectorwith5ormoreyearsofserviceMember
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- Details

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- Details

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Compensation Plans (Details)	1 Months Ended	3 Months Ended		6 Months Ended
Compensation Plans (Details)	Jul. 22, 2015 USD ($) shares	Jun. 30, 2015 USD ($) shares	Jun. 30, 2014 USD ($) shares	Jun. 30, 2015 USD ($) shares	Jun. 30, 2014 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense \| $				$ 13,215,000	$ 14,341,000
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation, Awards Other Than Options, Performance Measurement Period		3		3
Stock-based compensation expense \| $		$ 2,700,000	$ 3,600,000	$ 5,000,000	6,800,000
Unrecognized stock based compensation expense \| $		$ 13,000,000		13,000,000
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares Represented by Each RSU		1
Stock-based compensation expense \| $		$ 2,900,000	2,900,000	5,800,000	5,700,000
Unrecognized stock based compensation expense \| $		14,300,000		14,300,000
Shares Issued to the Board of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense \| $		$ 1,200,000	$ 1,200,000	$ 1,200,000	$ 1,200,000
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				1 year
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted				37,950	23,009
Shares Issued to the Board of Directors, Director with 5 or more years of service [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				5 years
Subsequent Event [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	320,753
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Total Fair Value \| $	$ 14,500,000
Multiplier Applied to PSU Awards Upon Settlement	1.00
Restricted Stock, Shares Issued Net of Shares for Tax Withholdings	188,279
Shares Paid for Tax Withholding for Share Based Compensation	100,683
Subsequent Event [Member] \| Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	356,246
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Total Fair Value \| $	$ 15,600,000
Restricted Stock, Shares Issued Net of Shares for Tax Withholdings	163,433
Shares Paid for Tax Withholding for Share Based Compensation	72,909
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted	236,342
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted		96,285	35,249
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription Rate		15.00%		15.00%
Share-based Compensation Arragement by Share-based Payment Award, Maximum Employee Subscription \| $		$ 25,000.00		$ 25,000.00
Share-based Compensation Arrangement by Share-Based Payment Award, Percent of Offering Date Price Paid		85.00%		85.00%
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		1,100,000		1,100,000
Minimum [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Awarded per Performance Stock Unit				0.00%
Maximum [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Awarded per Performance Stock Unit				200.00%