Business Segment Information (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended										12 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014		Dec. 31, 2013	Sep. 30, 2013		Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2014 segment	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting Information [Line Items]
Number of reportable segments											5
Segment Profit: Net Income (Loss)	$ 57,431	$ 64,520	$ 95,210	[1]	$ 82,252	$ 47,842	[2]	$ 58,495	$ 85,720	$ 67,944	$ 299,413	$ 260,001	$ 220,077
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)											6,631	4,589	4,169
Energy Marketing [Member] | Unbilled Revenues [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers											8,500
Energy Marketing [Member] | Margin [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)											$ 600

[1] Includes $3.6 million of income associated with a death benefit gain on life insurance proceeds recorded in the Corporate category.

[2] Includes a $4.7 million refund provision recorded in the Utility segment related to various issues raised in Distribution Corporation’s rate proceeding in New York.