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, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost		$ 2,120	$ 2,480	$ 4,241	$ 4,960
Interest Cost		9,594	8,252	19,189	16,503
Expected Return on Plan Assets		(15,591)	(15,429)	(31,184)	(30,857)
Amortization of Prior Service Cost (Credit)		206	235	413	469
Amortization of Losses		8,024	9,301	16,048	18,602
Net Amortization and Deferral For Regulatory Purposes (Including Volumetric Adjustments)	[1]	4,786	6,492	5,604	8,214
Net Periodic Benefit Cost		9,139	11,331	14,311	17,891
Other Post-Retirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost		380	458	760	915
Interest Cost		4,286	3,700	8,572	7,400
Expected Return on Plan Assets		(7,539)	(7,871)	(15,078)	(15,741)
Amortization of Prior Service Cost (Credit)		(107)	(107)	(214)	(214)
Amortization of Losses		1,490	2,639	2,980	5,279
Net Amortization and Deferral For Regulatory Purposes (Including Volumetric Adjustments)	[1]	6,565	6,250	10,536	9,858
Net Periodic Benefit Cost		$ 5,075	$ 5,069	$ 7,556	$ 7,497

[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.