Fair value of the assets less the liabilities of a derivative or group of derivatives.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13433-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13495-108611

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Regulatory Assets and Liabilities and Regulatory Matters (Details) - USD ($) $ in Thousands	Jan. 19, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Gas Utility
Regulatory Assets
Fair value of unrealized gains (losses)		$ (4,488)	$ (3,262)	$ (6,798)
Electric Utility
Regulatory Assets
Fair value of unrealized gains (losses)		$ (450)	$ (533)	$ (2,397)
Pennsylvania Public Utility Commission \| Subsequent Event
Regulatory Assets
Requested operating revenue increase	$ 58,600
Estimated time period for regulatory approval (in months)	9 months