Regulatory Assets and Liabilities and Regulatory Matters - Narrative (Details) - USD ($) $ in Thousands						1 Months Ended	3 Months Ended	12 Months Ended
	Oct. 20, 2017	Jul. 01, 2017	Oct. 14, 2016	Apr. 01, 2016	Apr. 01, 2015	Mar. 31, 2016	Dec. 31, 2017	Sep. 30, 2014	Sep. 30, 2017	Dec. 31, 2016
Minimum
Regulatory Assets
Average remaining depreciable lives of associated property.							1 year
Maximum
Regulatory Assets
Average remaining depreciable lives of associated property.							65 years
Pennsylvania PUC
Regulatory Assets
Distribution system improvement charge, percent of amount billed to customers							5.00%
Pennsylvania PUC | Maximum
Regulatory Assets
Distribution system improvement charge, percent of amount billed to customers								0.00%
Pennsylvania PUC | PNG
Regulatory Assets
Increase in annual base distribution rate	$ 11,250
Distribution system improvement charge, percent of amount billed to customers		7.50%
Pennsylvania PUC | PNG | Maximum
Regulatory Assets
Distribution system improvement charge, percent of amount billed to customers					0.00%
Pennsylvania PUC | UGI Gas
Regulatory Assets
Increase in annual base distribution rate			$ 27,000
Pennsylvania PUC | CPG
Regulatory Assets
Distribution system improvement charge, percent of amount billed to customers		7.50%
Pennsylvania PUC | CPG | Maximum
Regulatory Assets
Distribution system improvement charge, percent of amount billed to customers				0.00%		10.00%
Gas Utility
Regulatory Assets
Fair value of unrealized gains (losses)							$ (1,720)		$ 146	$ 6,927