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Commitments and Contingencies - Additional Information (Detail) (USD $)
 12 Months Ended
Mar. 31, 2015
GeneratingPlant
Mar. 31, 2014
Mar. 31, 2013
Product Liability Contingency [Line Items]      
Letters of credit outstanding, amount $ 9,200,000us-gaap_LettersOfCreditOutstandingAmount    
Contingently liable for performance, current 14,800,000exp_ContingentLiabilityForPerformanceBondsRequiredByStatesMunicipalitiesAndRelatedAgencies    
Outstanding guarantees 0us-gaap_GuarantyLiabilities    
Sale percentage of gypsum-grade recycled paperboard 90.00%exp_PercentageOfGypsumGradeRecycledPaperboard    
Number of plants 3exp_NumberOfManufacturingPlants    
Percentage of expected natural gas usage 25.00%exp_PercentageOfExpectedNaturalGasUsage    
Operating leases Rental expense $ 5,900,000us-gaap_LeaseAndRentalExpense $ 3,200,000us-gaap_LeaseAndRentalExpense $ 1,600,000us-gaap_LeaseAndRentalExpense
Minimum [Member]      
Product Liability Contingency [Line Items]      
Sale percentage of gypsum-grade recycled paperboard 15.00%exp_PercentageOfGypsumGradeRecycledPaperboard
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		    
Maximum [Member]      
Product Liability Contingency [Line Items]      
Sale percentage of gypsum-grade recycled paperboard 20.00%exp_PercentageOfGypsumGradeRecycledPaperboard
/ us-gaap_RangeAxis
= us-gaap_MaximumMember