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Plan Assets Related to Pension Benefits by Level within the Fair Value Hierarchy (Additional Information) (Details) (Pension Plans, Defined Benefit)
Dec. 31, 2014
Dec. 31, 2013
Pension Plans, Defined Benefit
    
Defined Benefit Plan Income Accrued On Plan Assets 0.60%sti_DefinedBenefitPlanIncomeAccruedOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember		 0.70%sti_DefinedBenefitPlanIncomeAccruedOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember