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, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost		$ 2,330	$ 2,120	$ 4,659	$ 4,241
Interest Cost		7,483	9,594	14,965	19,189
Expected Return on Plan Assets		(15,016)	(15,591)	(30,032)	(31,184)
Amortization of Prior Service Cost (Credit)		182	206	365	413
Amortization of Losses		9,846	8,024	19,692	16,048
Net Amortization and Deferral For Regulatory Purposes (Including Volumetric Adjustments)	[1]	5,519	4,786	7,047	5,604
Net Periodic Benefit Cost		10,344	9,139	16,696	14,311
Other Post-Retirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost		402	380	804	760
Interest Cost		3,228	4,286	6,457	8,572
Expected Return on Plan Assets		(7,308)	(7,539)	(14,616)	(15,078)
Amortization of Prior Service Cost (Credit)		(107)	(107)	(214)	(214)
Amortization of Losses		134	1,490	267	2,980
Net Amortization and Deferral For Regulatory Purposes (Including Volumetric Adjustments)	[1]	8,846	6,565	15,094	10,536
Net Periodic Benefit Cost		$ 5,195	$ 5,075	$ 7,792	$ 7,556

[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.