Financial Instruments Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	[1]	Mar. 31, 2018	Mar. 31, 2017
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Interest rate agreements fair value		$ 21,786	$ 4,144		$ 20,454	$ 95,271	[1]
Forward commodity contracts fair value	[2]	0	0		0	9,847	[1]
Interest rate agreements		458	86		835	173	[1]
Forward commodity contracts	[2]	0	0		0	(4,865)	[1]
Total other comprehensive income (loss) from hedging, net of tax		22,244	$ 4,230		21,289	$ 100,426	[1]
Regulated Segments Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate						37.00%
Nonregulated Segment Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate						39.00%
Expected Earnings [Line Items]
Expected Recognition in Earnings of Deferred Gain (Losses), Interest Rate Agreements		(49,114)			(49,114)
Next Twelve Months [Member]
Expected Earnings [Line Items]
Expected Recognition in Earnings of Deferred Gain (Losses), Interest Rate Agreements		(1,833)			(1,833)
Thereafter [Member]
Expected Earnings [Line Items]
Expected Recognition in Earnings of Deferred Gain (Losses), Interest Rate Agreements		$ (47,281)			$ (47,281)

[1] Utilizing an income tax rate ranging from 37 percent to 39 percent based on the effective rates in each taxing jurisdiction for the three and six-month period ended March 31, 2017.

[2] Due to the sale of AEM, these amounts are included in income from discontinued operations