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Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 9 Months Ended 12 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Sep. 30, 2018
Sep. 30, 2019
Summary Of Significant Accounting Policies [Line Items]            
Pension and Postretirement Benefit Costs in Other Income and Deductions $ 5,700 $ 6,200 $ 25,500 $ 28,600    
Gas stored underground $ (17,075)   (17,075)   $ (37,813)  
Capitalized costs of unproved properties excluded from amortization     $ 82,000   62,200  
Full cost ceiling test discount factor 10.00%   10.00%      
Amount Full Cost Ceiling Exceeds Book Value Of Oil And Gas Properties $ 566,800   $ 566,800      
Decrease estimated future net cash flows $ 23,900          
Antidilutive securities 120,546 1,095,838 122,327 316,279    
Reserve For Gas Replacement [Member]            
Summary Of Significant Accounting Policies [Line Items]            
Gas stored underground $ 16,251   $ 16,251   $ 0  
Non-performance Based Restricted Stock Units [Member]            
Summary Of Significant Accounting Policies [Line Items]            
Share based compensation other than options grants in period     112,608      
Granted in fiscal year, weighted average grant date fair value     $ 49.70      
Performance Shares [Member]            
Summary Of Significant Accounting Policies [Line Items]            
Share based compensation other than options grants in period     244,734      
Granted in fiscal year, weighted average grant date fair value     $ 55.67      
Subsequent Event [Member] | Reserve For Gas Replacement [Member]            
Summary Of Significant Accounting Policies [Line Items]            
Gas stored underground           $ 0
Guidance for Reclassification of Stranded Tax Effects [Member]            
Summary Of Significant Accounting Policies [Line Items]            
Cumulative Effect of Adoption of Authoritative Guidance 10,400   $ 10,400      
Guidance for Recognition and Measurement of Financial Assets and Liabilities [Member]            
Summary Of Significant Accounting Policies [Line Items]            
Cumulative Effect of Adoption of Authoritative Guidance $ 7,400   $ 7,400