Summary of Significant Accounting Policies - Summary of Property, Plant and Equipment by Classification (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Public Utilities, Allowance for Funds Used During Construction, Description	1869586
Property, plant and equipment
Total property, plant and equipment	$ 1,569,683	$ 1,312,117
Less: Accumulated depreciation and amortization	(294,295)	(270,599)
Plus: Construction work in progress	108,584	84,509
Net property, plant and equipment	1,383,972	1,126,027
Natural Gas Distribution [Member] | Delmarva and Florida [Member]
Property, plant and equipment
Total property, plant and equipment	657,630	589,149
Natural Gas Transmission [Member] | Delmarva Peninsula, Pennsylvania and Florida [Member]
Property, plant and equipment
Total property, plant and equipment	537,654	384,360
Natural Gas Transmission [Member] | OHIO
Property, plant and equipment
Total property, plant and equipment	70,225	66,037
Electric distribution | Florida
Property, plant and equipment
Total property, plant and equipment	102,133	100,227
Propane Operations [Member] | Mid-Atlantic and Florida [Member]
Property, plant and equipment
Total property, plant and equipment	123,632	108,177
Electricity and Steam Generation [Member] | Florida
Property, plant and equipment
Total property, plant and equipment	35,239	35,239
Mobile CNG Utility and Pipeline Solutions [Member] | Florida
Property, plant and equipment
Total property, plant and equipment	7,240	0
Other unregulated energy | Other [Member]
Property, plant and equipment
Total property, plant and equipment	1,346	1,229
Other
Property, plant and equipment
Total property, plant and equipment	$ 34,584	$ 27,699