Regulatory Assets and Liabilities and Regulatory Matters - Additional Information (Details) - USD ($) $ in Thousands											1 Months Ended	12 Months Ended
	Oct. 20, 2017	Jul. 01, 2017	Jan. 19, 2017	Jan. 01, 2017	Oct. 19, 2016	Oct. 14, 2016	Jun. 30, 2016	Apr. 01, 2016	Jan. 19, 2016	Apr. 01, 2015	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2016
Regulatory Assets
Unrealized gains (losses) on derivative financial instruments contracts												$ 146			$ 4,263
Capitalized project costs															5,830
Project costs expensed in prior periods													$ 5,375
Information Technology
Regulatory Assets
Associated increase to utility property, plant and equipment															2,755
Pennsylvania Public Utility Commission
Regulatory Assets
Requested operating revenue increase			$ 21,700
Maximum period post petition to file general rate filing												5 years
Distribution system improvement charge, percent of amount billed to customers														0.00%
Pennsylvania Public Utility Commission | PNG
Regulatory Assets
Distribution system improvement charge, percent of amount billed to customers		7.50%								0.00%
Pennsylvania Public Utility Commission | PNG | Subsequent Event
Regulatory Assets
Approved operating revenue increase	$ 11,250
Pennsylvania Public Utility Commission | UGI Gas
Regulatory Assets
Requested operating revenue increase									$ 58,600
Amount of operating revenue increase							$ 27,000
Approved operating revenue increase						$ 27,000
Pennsylvania Public Utility Commission | CPG
Regulatory Assets
Distribution system improvement charge, percent of amount billed to customers		7.50%						0.00%
Removal Costs
Regulatory Assets
Period to recover costs related to regulatory assets												5 years
Deferred Project Costs
Regulatory Assets
Associated increase to utility regulatory assets															$ 3,075
Minimum
Regulatory Assets
Average remaining depreciable lives of the associated property												1 year
Maximum
Regulatory Assets
Average remaining depreciable lives of the associated property												65 years
Maximum | Pennsylvania Public Utility Commission
Regulatory Assets
Distribution system improvement charge, percent of amount billed to customers				5.00%							5.00%
Maximum | Pennsylvania Public Utility Commission | PNG
Regulatory Assets
Distribution system improvement charge, percent of amount billed to customers											10.00%
Maximum | Pennsylvania Public Utility Commission | CPG
Regulatory Assets
Distribution system improvement charge, percent of amount billed to customers											10.00%
Maximum | Postretirement benefits overcollections
Regulatory Assets
Regulatory liability, period over which overcollections will be refunded to customers					10 years