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, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost		$ 2,480	$ 2,992	$ 4,960	$ 5,984
Interest Cost		8,252	9,596	16,503	19,192
Expected Return on Plan Assets		(15,429)	(14,929)	(30,857)	(29,859)
Amortization of Prior Service Cost (Credit)		235	264	469	529
Amortization of Losses		9,301	10,672	18,602	21,343
Net Amortization and Deferral For Regulatory Purposes (Including Volumetric Adjustments)	[1]	6,492	6,234	8,214	6,770
Net Periodic Benefit Cost		11,331	14,829	17,891	23,959
Other Post-Retirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost		458	612	915	1,224
Interest Cost		3,700	4,752	7,400	9,504
Expected Return on Plan Assets		(7,871)	(7,865)	(15,741)	(15,729)
Amortization of Prior Service Cost (Credit)		(107)	(107)	(214)	(214)
Amortization of Losses		2,639	4,604	5,279	9,207
Net Amortization and Deferral For Regulatory Purposes (Including Volumetric Adjustments)	[1]	6,250	3,790	9,858	5,102
Net Periodic Benefit Cost		$ 5,069	$ 5,786	$ 7,497	$ 9,094

[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.