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Components of Gas Inventory (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Public Utilities, Inventory [Line Items]    
Weighted average cost inventory amount $ 1.1us-gaap_WeightedAverageCostInventoryAmount $ 1.2us-gaap_WeightedAverageCostInventoryAmount
Liquefied Natural Gas & Other    
Public Utilities, Inventory [Line Items]    
Weighted average cost inventory amount 0.1us-gaap_WeightedAverageCostInventoryAmount
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
0.1us-gaap_WeightedAverageCostInventoryAmount
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
Natural Gas    
Public Utilities, Inventory [Line Items]    
Weighted average cost inventory amount 0.8us-gaap_WeightedAverageCostInventoryAmount
/ us-gaap_PublicUtilitiesInventoryAxis
= us-gaap_PublicUtilitiesInventoryNaturalGasMember
0.8us-gaap_WeightedAverageCostInventoryAmount
/ us-gaap_PublicUtilitiesInventoryAxis
= us-gaap_PublicUtilitiesInventoryNaturalGasMember
Propane    
Public Utilities, Inventory [Line Items]    
Weighted average cost inventory amount $ 0.2us-gaap_WeightedAverageCostInventoryAmount
/ us-gaap_PublicUtilitiesInventoryAxis
= us-gaap_PublicUtilitiesInventoryPropaneMember
$ 0.3us-gaap_WeightedAverageCostInventoryAmount
/ us-gaap_PublicUtilitiesInventoryAxis
= us-gaap_PublicUtilitiesInventoryPropaneMember