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Fair Value Measurements (Financial Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments $ 278,565us-gaap_AvailableForSaleSecuritiesCurrent $ 251,254us-gaap_AvailableForSaleSecuritiesCurrent
Fair Value, Measurements, Recurring [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Mutual funds 765swc_MutualFunds
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Fair Value, Measurements, Recurring [Member] | Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Mutual funds 765swc_MutualFunds
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Fair Value, Measurements, Recurring [Member] | Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Mutual funds 0swc_MutualFunds
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/ us-gaap_FairValueByMeasurementFrequencyAxis
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Fair Value, Measurements, Recurring [Member] | Level 3 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Mutual funds 0swc_MutualFunds
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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Fair Value, Measurements, Recurring [Member] | Federal Agency Notes [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments 168,582us-gaap_AvailableForSaleSecuritiesCurrent
/ us-gaap_EligibleItemOrGroupForFairValueOptionAxis
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Fair Value, Measurements, Recurring [Member] | Federal Agency Notes [Member] | Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments 0us-gaap_AvailableForSaleSecuritiesCurrent
/ us-gaap_EligibleItemOrGroupForFairValueOptionAxis
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/ us-gaap_FairValueByMeasurementFrequencyAxis
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Fair Value, Measurements, Recurring [Member] | Federal Agency Notes [Member] | Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments 168,582us-gaap_AvailableForSaleSecuritiesCurrent
/ us-gaap_EligibleItemOrGroupForFairValueOptionAxis
= swc_FederalAgencyNotesMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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Fair Value, Measurements, Recurring [Member] | Federal Agency Notes [Member] | Level 3 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments 0us-gaap_AvailableForSaleSecuritiesCurrent
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Fair Value, Measurements, Recurring [Member] | Commercial paper [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments 109,983us-gaap_AvailableForSaleSecuritiesCurrent
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Fair Value, Measurements, Recurring [Member] | Commercial paper [Member] | Level 1 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments 0us-gaap_AvailableForSaleSecuritiesCurrent
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= us-gaap_FairValueMeasurementsRecurringMember
Fair Value, Measurements, Recurring [Member] | Commercial paper [Member] | Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments 109,983us-gaap_AvailableForSaleSecuritiesCurrent
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Fair Value, Measurements, Recurring [Member] | Commercial paper [Member] | Level 3 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Investments $ 0us-gaap_AvailableForSaleSecuritiesCurrent
/ us-gaap_EligibleItemOrGroupForFairValueOptionAxis
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