Business Segment Information (Financial Segment Information By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenue	$ 444,188	$ 490,247
Segment Profit: Net Income (Loss)	86,591	102,660
Segment Assets	6,702,658		$ 6,462,157
Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	444,188	490,247
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Revenue	165,939	162,876
Segment Profit: Net Income (Loss)	23,977	38,214
Segment Assets	2,059,681		1,972,776
Exploration And Production [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	165,939	162,876
Exploration And Production [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Pipeline And Storage [Member]
Segment Reporting Information [Line Items]
Revenue	72,220	77,069
Segment Profit: Net Income (Loss)	18,105	25,102
Segment Assets	1,926,766		1,893,514
Pipeline And Storage [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	48,969	54,218
Pipeline And Storage [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	23,251	22,851
Gathering [Member]
Segment Reporting Information [Line Items]
Revenue	34,788	29,690
Segment Profit: Net Income (Loss)	15,944	14,183
Segment Assets	559,064		547,995
Gathering [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	0	0
Gathering [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	34,788	29,690
Utility [Member]
Segment Reporting Information [Line Items]
Revenue	196,825	222,657
Segment Profit: Net Income (Loss)	26,583	25,649
Segment Assets	2,043,246		1,991,338
Utility [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	194,910	220,012
Utility [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	1,915	2,645
Total Reportable Segments [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	84,609	103,148
Segment Assets	6,588,757		6,405,623
Total Reportable Segments [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	409,818	437,106
Total Reportable Segments [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	59,954	55,186
All Other [Member]
Segment Reporting Information [Line Items]
Revenue	34,412	53,419
Segment Profit: Net Income (Loss)	371	82
Segment Assets	143,890		122,241
All Other [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	34,235	53,087
All Other [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	177	332
Corporate And Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	(59,996)	(55,464)
Segment Profit: Net Income (Loss)	1,611	(570)
Segment Assets	(29,989)		$ (65,707)
Corporate And Intersegment Eliminations [Member] | Revenue from External Customers [Member]
Segment Reporting Information [Line Items]
Revenue	135	54
Corporate And Intersegment Eliminations [Member] | Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Revenue	$ (60,131)	$ (55,518)