Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Summary of Property, Plant and Equipment by Classification

A summary of property, plant and equipment by classification as of December 31, 2017 and 2016 is provided in the following table:



	As of December 31,
(in thousands)	2017			2016
Property, plant and equipment
Regulated Energy
Natural gas distribution – Delmarva Peninsula	$	234,654		$	220,083
Natural gas distribution – Florida	354,495			331,281
Natural gas transmission – Delmarva	357,264			285,746
Natural gas transmission – Florida	27,096			27,018
Electric distribution – Florida	100,227			93,553
Unregulated Energy
Propane distribution – Delmarva Peninsula	79,139			73,686
Propane distribution – Florida	29,038			26,359
Other unregulated natural gas services – Ohio	66,037			61,383
CHP - Florida	35,239			35,237
Other unregulated energy	1,229			135
Other	27,699			21,114
Total property, plant and equipment	1,312,117			1,175,595
Less: Accumulated depreciation and amortization	(270,599		)	(245,207		)
Plus: Construction work in progress	84,509			56,276
Net property, plant and equipment	$	1,126,027		$	986,664

Average Depreciation Rates

We compute depreciation expense for our regulated operations by applying composite, annual rates, as approved by the respective regulatory bodies. The following table shows the average depreciation rates used for regulated operations during the years ended December 31, 2017, 2016 and 2015:



	2017	2016	2015
Natural gas distribution – Delmarva Peninsula	2.5%	2.5%	2.4%
Natural gas distribution – Florida	2.9%	2.9%	2.9%
Natural gas transmission – Delmarva Peninsula	2.8%	2.7%	2.7%
Natural gas transmission – Florida	3.5%	3.9%	4.0%
Electric distribution – Florida	3.4%	3.5%	3.5%

Estimated Useful Lives of Assets

For our unregulated operations, we compute depreciation expense on a straight-line basis over the following estimated useful lives of the assets:



Asset Description	Useful Life
Propane distribution mains	10-37 years
Propane bulk plants and tanks	10-40 years
Propane equipment	5-33 years
Meters and meter installations	5-33 years
Measuring and regulating station equipment	5-37 years
Natural gas pipelines	45 years
Natural gas right of ways	Perpetual
CHP plant	30 years
Natural gas processing equipment	20-25 years
Office furniture and equipment	3-10 years
Transportation equipment	4-20 years
Structures and improvements	5-45 years
Other	Various