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Contingencies - Additional Information (Detail)
$ in Millions
Aug. 13, 2015
USD ($)
Loss Contingencies [Line Items]  
Remedial action objective time frame 10 years
Capital cost  
Loss Contingencies [Line Items]  
Remedial alternative, maximum $ 12.9
Remedial alternative, EPA preferred remedy 5.4
Operating cost  
Loss Contingencies [Line Items]  
Remedial alternative, maximum 0.6
Maintenance cost  
Loss Contingencies [Line Items]  
Remedial alternative, EPA preferred remedy $ 1.8