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Asset Retirement Obligations (Details) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013
Asset Retirement Obligations [Line Items] |  |
Asset Retirement Obligations Assets Held-for-sale Noncurrent | $ 438,000 sm_AssetRetirementObligationsAssetsHeldForSaleNoncurrent |
Asset Retirement Obligation, Current | 1,300,000 us-gaap_AssetRetirementObligationCurrent | 2,500,000 us-gaap_AssetRetirementObligationCurrent
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] |  |
Asset Retirement Obligation: Beginning of Year | 121,186,000 us-gaap_AssetRetirementObligation | 120,518,000 us-gaap_AssetRetirementObligation
Asset Retirement Obligation, Liabilities Incurred | 13,506,000 us-gaap_AssetRetirementObligationLiabilitiesIncurred | 18,682,000 us-gaap_AssetRetirementObligationLiabilitiesIncurred
Asset Retirement Obligation, Liabilities Settled | (11,372,000)us-gaap_AssetRetirementObligationLiabilitiesSettled | (33,129,000)us-gaap_AssetRetirementObligationLiabilitiesSettled
Asset Retirement Obligation, Accretion Expense | 6,090,000 us-gaap_AssetRetirementObligationAccretionExpense | 5,997,000 us-gaap_AssetRetirementObligationAccretionExpense
Asset Retirement Obligation, Revision of Estimate | (7,286,000)us-gaap_AssetRetirementObligationRevisionOfEstimate | 9,118,000 us-gaap_AssetRetirementObligationRevisionOfEstimate
Asset Retirement Obligation: End of Year | $ 122,124,000 us-gaap_AssetRetirementObligation | $ 121,186,000 us-gaap_AssetRetirementObligation
Minimum [Member] |  |
Asset Retirement Obligations [Line Items] |  |
Fair Value Assumptions, Risk Free Interest Rate | 5.50%us-gaap_FairValueAssumptionsRiskFreeInterestRate / us-gaap_RangeAxis = us-gaap_MinimumMember |
Maximum [Member] |  |
Asset Retirement Obligations [Line Items] |  |
Fair Value Assumptions, Risk Free Interest Rate | 12.00%us-gaap_FairValueAssumptionsRiskFreeInterestRate / us-gaap_RangeAxis = us-gaap_MaximumMember |

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- Definition Noncurrent portion of the carrying amount of a liability for an asset retirement obligation for an asset held for sale. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References No definition available. + Details
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- Definition The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Asset Retirement Obligation -URI http://asc.fasb.org/extlink&oid=6505190 + Details
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- Definition Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Current portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Amount of asset retirement obligations incurred during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Amount of the Increase or Decrease in the amount of the asset retirement obligation during the current period for changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(4) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Risk-free interest rate assumption used in valuing an instrument. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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