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Commitments and Contingencies (Details) (USD $)
1 Months Ended 22 Months Ended 3 Months Ended
Oct. 31, 2014
Mar. 31, 2015
Mar. 31, 2015
Loss Contingencies [Line Items]      
Environmental remediation expense   $ 130,800,000us-gaap_EnvironmentalRemediationExpense  
Gross proceeds from insurance settlement, operating activities 25,000,000.0dnr_GrossProceedsfromInsuranceSettlementOperatingActivities    
Minimum      
Loss Contingencies [Line Items]      
Estimated percentage of environmental remediation expense estimate to be recovered through insurance proceeds   33.33333%dnr_EstimatedPercentageofEnvironmentalRemediationExpenseEstimatetobeRecoveredThroughInsuranceProceeds
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
33.33333%dnr_EstimatedPercentageofEnvironmentalRemediationExpenseEstimatetobeRecoveredThroughInsuranceProceeds
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Loss Contingency, Damages Sought, Value     $ 200,000,000us-gaap_LossContingencyDamagesSoughtValue
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Maximum      
Loss Contingencies [Line Items]      
Estimated percentage of environmental remediation expense estimate to be recovered through insurance proceeds   66.66667%dnr_EstimatedPercentageofEnvironmentalRemediationExpenseEstimatetobeRecoveredThroughInsuranceProceeds
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
66.66667%dnr_EstimatedPercentageofEnvironmentalRemediationExpenseEstimatetobeRecoveredThroughInsuranceProceeds
/ us-gaap_RangeAxis
= us-gaap_MaximumMember