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Regulatory Assets and Liabilities and Regulatory Matters - Narrative (Details) - USD ($)
$ in Thousands
1 Months Ended 9 Months Ended 12 Months Ended
Oct. 20, 2017
Jul. 01, 2017
Jan. 19, 2017
Jan. 01, 2017
Oct. 14, 2016
Apr. 01, 2016
Apr. 01, 2015
Mar. 31, 2016
Jun. 30, 2017
Sep. 30, 2014
Sep. 30, 2016
Jun. 30, 2016
Pennsylvania PUC                        
Regulatory Assets                        
Maximum period post petition to file general rate filing (in years)                 5 years      
Pennsylvania PUC | Maximum                        
Regulatory Assets                        
Distribution system improvement charge, percent of amount billed to customers       5.00%       5.00%   0.00%    
Pennsylvania PUC | PNG                        
Regulatory Assets                        
Requested operating revenue increase     $ 21,700                  
Pennsylvania PUC | PNG | Subsequent Event                        
Regulatory Assets                        
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% 10.00%        
Pennsylvania PUC | PNG | Forecast                        
Regulatory Assets                        
Increase in annual base distribution rate $ 11,250                      
Pennsylvania PUC | UGI Gas                        
Regulatory Assets                        
Increase in annual base distribution rate         $ 27,000              
Pennsylvania PUC | CPG | Subsequent Event                        
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)                 $ (73)   $ 4,263 $ 5,483