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Fair Value Measurements (Financial Assets And Liabilities Measured At Fair Value On A Nonrecurring Basis) (Details) (Fair Value, Measurements, Nonrecurring [Member], USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Certain Marathon real estate properties   $ 754us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
Long-term investments 841us-gaap_InvestmentsFairValueDisclosure 896us-gaap_InvestmentsFairValueDisclosure
Level 1 [Member]
    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Certain Marathon real estate properties   0us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Long-term investments 841us-gaap_InvestmentsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember		 896us-gaap_InvestmentsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Level 2 [Member]
    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Certain Marathon real estate properties   0us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Long-term investments 0us-gaap_InvestmentsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember		 0us-gaap_InvestmentsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Level 3 [Member]
    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Certain Marathon real estate properties   754us-gaap_PropertyPlantAndEquipmentFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Long-term investments 0us-gaap_InvestmentsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember		 0us-gaap_InvestmentsFairValueDisclosure
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
1.875% Convertible Debentures [Member]
    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Convertible debentures, fair value 2,245us-gaap_ConvertibleDebtFairValueDisclosures
/ us-gaap_DebtInstrumentAxis
= swc_OnePointEightSevenFivePercentageConvertibleDebenturesMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember		 2,245us-gaap_ConvertibleDebtFairValueDisclosures
/ us-gaap_DebtInstrumentAxis
= swc_OnePointEightSevenFivePercentageConvertibleDebenturesMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
1.875% Convertible Debentures [Member] | Level 1 [Member]
    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Convertible debentures, fair value 0us-gaap_ConvertibleDebtFairValueDisclosures
/ us-gaap_DebtInstrumentAxis
= swc_OnePointEightSevenFivePercentageConvertibleDebenturesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember		 0us-gaap_ConvertibleDebtFairValueDisclosures
/ us-gaap_DebtInstrumentAxis
= swc_OnePointEightSevenFivePercentageConvertibleDebenturesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
1.875% Convertible Debentures [Member] | Level 2 [Member]
    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Convertible debentures, fair value 2,245us-gaap_ConvertibleDebtFairValueDisclosures
/ us-gaap_DebtInstrumentAxis
= swc_OnePointEightSevenFivePercentageConvertibleDebenturesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember		 2,245us-gaap_ConvertibleDebtFairValueDisclosures
/ us-gaap_DebtInstrumentAxis
= swc_OnePointEightSevenFivePercentageConvertibleDebenturesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
1.875% Convertible Debentures [Member] | Level 3 [Member]
    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Convertible debentures, fair value 0us-gaap_ConvertibleDebtFairValueDisclosures
/ us-gaap_DebtInstrumentAxis
= swc_OnePointEightSevenFivePercentageConvertibleDebenturesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember		 0us-gaap_ConvertibleDebtFairValueDisclosures
/ us-gaap_DebtInstrumentAxis
= swc_OnePointEightSevenFivePercentageConvertibleDebenturesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
1.75% Convertible Debentures [Member]
    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Convertible debentures, fair value 322,363us-gaap_ConvertibleDebtFairValueDisclosures
/ us-gaap_DebtInstrumentAxis
= swc_OnePointSevenFivePercentageConvertibleDebenturesMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember		 303,108us-gaap_ConvertibleDebtFairValueDisclosures
/ us-gaap_DebtInstrumentAxis
= swc_OnePointSevenFivePercentageConvertibleDebenturesMember
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
1.75% Convertible Debentures [Member] | Level 1 [Member]
    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Convertible debentures, fair value 0us-gaap_ConvertibleDebtFairValueDisclosures
/ us-gaap_DebtInstrumentAxis
= swc_OnePointSevenFivePercentageConvertibleDebenturesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember		 0us-gaap_ConvertibleDebtFairValueDisclosures
/ us-gaap_DebtInstrumentAxis
= swc_OnePointSevenFivePercentageConvertibleDebenturesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
1.75% Convertible Debentures [Member] | Level 2 [Member]
    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Convertible debentures, fair value 322,363us-gaap_ConvertibleDebtFairValueDisclosures
/ us-gaap_DebtInstrumentAxis
= swc_OnePointSevenFivePercentageConvertibleDebenturesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember		 303,108us-gaap_ConvertibleDebtFairValueDisclosures
/ us-gaap_DebtInstrumentAxis
= swc_OnePointSevenFivePercentageConvertibleDebenturesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
1.75% Convertible Debentures [Member] | Level 3 [Member]
    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Convertible debentures, fair value $ 0us-gaap_ConvertibleDebtFairValueDisclosures
/ us-gaap_DebtInstrumentAxis
= swc_OnePointSevenFivePercentageConvertibleDebenturesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember		 $ 0us-gaap_ConvertibleDebtFairValueDisclosures
/ us-gaap_DebtInstrumentAxis
= swc_OnePointSevenFivePercentageConvertibleDebenturesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember