Summary Of Significant Accounting Policies (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended				9 Months Ended								9 Months Ended		9 Months Ended		9 Months Ended		3 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Sep. 30, 2011	Sep. 30, 2010	Mar. 31, 2011	Jun. 30, 2012 Utility [Member]	Jun. 30, 2011 Offshore Oil and Natural Gas Properties [Member]	Jun. 30, 2012 Stock Options [Member]	Jun. 30, 2012 Restricted Share Awards [Member]	Jun. 30, 2012 Restricted Stock Units [Member]	Jun. 30, 2012 Nonperformance Based Stock Appreciation Right [Member]	Jun. 30, 2012 Exchange-Traded Futures Contracts [Member]	Sep. 30, 2011 Exchange-Traded Futures Contracts [Member]	Sep. 30, 2011 Over-The-Counter Crude Oil Swap Agreements [Member]	Jun. 30, 2011 Reclassification Of Regulatory Liabilities To Regulatory AssetsDue To Change From Gross To Net Methodology [Member]	Sep. 30, 2011 Reclassification Of Regulatory Liabilities To Regulatory AssetsDue To Change From Gross To Net Methodology [Member]	Jun. 30, 2011 Reclassification Of Regulatory Assets To Other Current Assets [Member]	Sep. 30, 2011 Reclassification Of Regulatory Assets To Other Current Assets [Member]	Jun. 30, 2011 Reclassification Of Regulatory Liabilities To Other Accruals and Current Liabilities [Member]	Sep. 30, 2011 Reclassification Of Regulatory Liabilities To Other Accruals and Current Liabilities [Member]	Mar. 31, 2011 Sale Of Equity Method Investee [Member]
Summary Of Significant Accounting Policies [Line Items]
Equity Method Investment, Ownership Percentage							50.00%
Sale of equity method investment			$ 0	$ 59,365,000																			$ 59,400,000
Gain on sale of equity method investment			0	50,879,000																			50,900,000
Regulatory Assets																		63,700,000
Change in other liabilities			25,338,000	(17,382,000)													1,900,000				(300,000)
Other Accruals and Current Liabilities	160,899,000		160,899,000		108,636,000																	13,800,000
Change in other assets			12,796,000	(8,582,000)													(1,900,000)		(13,600,000)
Other current assets	48,246,000		48,246,000		64,923,000															26,600,000
Change in prepayments and other current assets.			(18,190,000)	(83,541,000)															13,600,000
Change in other accruals and current liabilities			17,083,000	36,446,000																	300,000
Accrued capital expenditure, non-cash investing activity			98,400,000	66,600,000	72,200,000	55,500,000
Hedging collateral deposits	3,392,000		3,392,000		19,701,000									3,400,000	5,500,000	14,200,000
Gas stored underground - current	24,787,000		24,787,000		54,325,000			30,500,000
Capitalized costs of unproved properties excluded from amortization			147,800,000		226,300,000
Full cost ceiling test discount factor	10.00%		10.00%
Amount full cost ceiling exceeds book value of oil and gas properties	107,000,000		107,000,000
Antidilutive securities	976,870	6,512	833,170	0
Stock options granted										0
Share based compensation other than options grants in period											41,525	68,450	166,000
Share based compensation arrangement by share based payment award other than options grants in period weighted average grant date excise price													$ 55.09
Granted in fiscal year, weighted average grant date fair value											$ 55.09	$ 47.10	$ 11.20
Tax Benefit Total Not Realized Due To Tax Loss Carryforwards	32,200,000		32,200,000		19,100,000
Proceeds from the sale of properties			$ 0	$ 69,435,000	$ 55,400,000				$ 61,800,000