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Retirement Plans (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Multiemployer Plans [Line Items]      
Retirement plan expense $ 1.6us-gaap_PensionAndOtherPostretirementBenefitExpense $ 1.5us-gaap_PensionAndOtherPostretirementBenefitExpense $ 1.5us-gaap_PensionAndOtherPostretirementBenefitExpense
Steelworkers Pension Trust [Member] | Maximum [Member]      
Multiemployer Plans [Line Items]      
Company contributions as a percentage of all contributions 5.00%us-gaap_MultiemployerPlansCollectiveBargainingArrangementPercentageOfContributions
/ us-gaap_MultiemployerPlanNameAxis
= usap_SteelworkersPensionTrustMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember