Business Segment Information (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Dec. 31, 2013 segment	Dec. 31, 2012
Segment Reporting Information [Line Items]
Number of reportable segments	5
Net income	$ 82,252	$ 67,944
Energy Marketing [Member]
Segment Reporting Information [Line Items]
Net income	1,604	495
Energy Marketing [Member] | Unbilled Revenues [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	25,500
Energy Marketing [Member] | Margin [Member]
Segment Reporting Information [Line Items]
Net income	$ 1,300