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Components of Gas Inventory (Detail) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2014
Dec. 31, 2013
Mar. 31, 2013
Public Utilities, Inventory [Line Items]      
Weighted average cost inventory amount $ 0.6 $ 1.2 $ 0.5
Natural Gas
     
Public Utilities, Inventory [Line Items]      
Weighted average cost inventory amount 0.2 0.8  
Propane
     
Public Utilities, Inventory [Line Items]      
Weighted average cost inventory amount 0.1 0.3 0.3
Liquefied Natural Gas & Other
     
Public Utilities, Inventory [Line Items]      
Weighted average cost inventory amount $ 0.3 $ 0.1 $ 0.2