Summary of Significant Accounting Policies - Summary of Property, Plant and Equipment by Classification (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Property, plant and equipment
Total property, plant and equipment	$ 788,791	$ 675,714
Less: Accumulated depreciation and amortization	(174,148)	(155,378)
Plus: Construction work in progress	16,603	21,445
Net property, plant and equipment	631,246	541,781
Natural gas distribution | Delmarva
Property, plant and equipment
Total property, plant and equipment	179,724	149,558
Natural gas distribution | Florida
Property, plant and equipment
Total property, plant and equipment	199,289	170,943
Natural gas transmission
Property, plant and equipment
Total property, plant and equipment	242,163	202,968
Electric distribution | Florida
Property, plant and equipment
Total property, plant and equipment	70,346	61,960
Propane distribution | Delmarva
Property, plant and equipment
Total property, plant and equipment	54,865	53,156
Propane distribution | Florida
Property, plant and equipment
Total property, plant and equipment	20,829	16,823
Other unregulated energy
Property, plant and equipment
Total property, plant and equipment	573	239
Other
Property, plant and equipment
Total property, plant and equipment	$ 21,002	$ 20,067