Components of Gas Inventory (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Public Utilities, Inventory [Line Items]
Weighted average cost inventory amount	$ 0.8	$ 1.2	$ 0.8
Natural Gas
Public Utilities, Inventory [Line Items]
Weighted average cost inventory amount	0.5	0.8	0.4
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	$ 0.2	$ 0.1	$ 0.1