Business Segment Information (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 segment	Mar. 31, 2013
Segment Reporting Information [Line Items]
Number of reportable segments			5
Segment Profit: Net Income (Loss)	$ 95,211	$ 85,720	$ 177,463	$ 153,664
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	3,765	4,283	5,369	4,778
Energy Marketing [Member] | Unbilled Revenues [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	8,200		33,700
Energy Marketing [Member] | Margin [Member]
Segment Reporting Information [Line Items]
Segment Profit: Net Income (Loss)	$ (400)		$ 900