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Commitments and Contingencies (Insurance Coverage) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2013
Mar. 31, 2016
Loss Contingencies [Line Items]        
Business insurance programs high deductible limits per occurrence $ 1arg_GeneralLiabilityInsuranceHighDeductibleLimitsPerOccurrence $ 1arg_GeneralLiabilityInsuranceHighDeductibleLimitsPerOccurrence $ 1arg_GeneralLiabilityInsuranceHighDeductibleLimitsPerOccurrence  
Self-insured medical benefits reserve 13.8us-gaap_AccruedInsuranceCurrent 12.9us-gaap_AccruedInsuranceCurrent    
Scenario, Forecast [Member]        
Loss Contingencies [Line Items]        
Business insurance programs high deductible limits per occurrence       $ 1arg_GeneralLiabilityInsuranceHighDeductibleLimitsPerOccurrence
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember