Retirement Plan And Other Post-Retirement Benefits (Components Of Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost		$ 2,992	$ 2,928	$ 5,984	$ 5,855
Interest Cost		9,596	10,579	19,192	21,158
Expected Return on Plan Assets		(14,929)	(14,842)	(29,859)	(29,685)
Amortization of Prior Service Cost (Credit)		264	308	529	617
Amortization of Losses		10,672	8,062	21,343	16,124
Net Amortization and Deferral For Regulatory Purposes (Including Volumetric Adjustments)	[1]	6,234	5,609	6,770	7,516
Net Periodic Benefit Cost		14,829	12,644	23,959	21,585
Other Post-Retirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost		612	583	1,224	1,166
Interest Cost		4,752	5,096	9,504	10,193
Expected Return on Plan Assets		(7,865)	(7,883)	(15,729)	(15,768)
Amortization of Prior Service Cost (Credit)		(107)	(228)	(214)	(456)
Amortization of Losses		4,604	1,382	9,207	2,765
Net Amortization and Deferral For Regulatory Purposes (Including Volumetric Adjustments)	[1]	3,790	6,599	5,102	10,720
Net Periodic Benefit Cost		$ 5,786	$ 5,549	$ 9,094	$ 8,620

[1] The Company’s policy is to record retirement plan and other post-retirement benefit costs in the Utility segment on a volumetric basis to reflect the fact that the Utility segment experiences higher throughput of natural gas in the winter months and lower throughput of natural gas in the summer months.