Summary Of Significant Accounting Policies (Narrative) (Details) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2011	Mar. 31, 2011	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2011
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Proceeds from Sale of Unconsolidated Subsidiaries	$ 59,400,000		$ 0		$ 0		$ 59,365,000
Gain on Sale of Unconsolidated Subsidiaries	50,900,000		0		0		50,879,000
Full cost ceiling test discount factor			10.00%
Proceeds from sale of properties			0		0		63,501,000
Asset retirement obligation		37,500,000
Goodwill			5,476,000		5,476,000
Loss related to mark-to-market adjustments associated with cash flow hedges			(2,000,000)		0		0
Unrealized gain on derivative financial instruments to be reclassified after twelve months			15,500,000
Loss related to mark-to-market adjustments associated with certain derivative instruments			(1,700,000)
Revisions to decrease operating cash flows and increase investing cash flows					1,800,000		6,600,000
Hedging collateral deposits			1,094,000	[1]	364,000	[1]
Customer advances			21,959,000		24,055,000
Customer security deposits			16,183,000		17,942,000
Antidilutive securities			181,418		844,872		0
Tax benefit realized from exercise of stock options and SARs			4,400,000		14,200,000		19,000,000
Tax benefit recorded from exercise of stock options			700,000		600,000		400,000
Stock-based compensation expense			11,500,000		7,200,000		6,700,000
Tax benefit related to stock-based compensation expense			4,600,000		2,900,000		2,700,000
Capitalized stock-based compensation costs			100,000		0		0
Number of shares subject to option, granted			0
Increase (decrease) estimated future net cash flows			71,600,000		128,400,000		35,400,000
Amount full cost ceiling exceeds book value of oil and gas properties			159,400,000
Accumulated losses			56,293,000		100,561,000
Gas stored underground - current			51,484,000		49,795,000
Prior service credit			300,000		400,000
Regulated Reacquisition of Debt Cost Weighted Average Amortization Period			6 years
Unrealized gain on derivative financial instruments to be reclassified within twelve months			15,200,000
Accumulated Losses [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated losses			56,600,000		100,900,000
Oil and Gas Properties [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Proceeds from sale of properties							55,400,000
Seneca Energy And Model City [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity method investment ownership percentage	50.00%	50.00%
Stock Options [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Options, exercises in period, total intrinsic value			11,600,000		13,500,000		44,600,000
Number of options vested during period			0		0		0
Proceeds from stock options exercised			2,600,000		7,600,000		9,500,000
Number of shares subject to option, granted			0		0		0
Unrecognized compensation expense			0
Restricted Share Awards [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Share based compensation other than options grants in period			0		41,525		47,250
Granted in fiscal year, weighted average grant date fair value			$ 0.00		$ 55.09		$ 63.98
Unrecognized compensation expense			2,200,000
Unrecognized compensation expense recognized weighted average period			2 years 7 months 6 days
Equity instruments other than options, vested in period			34,582
Stock Appreciation Rights SARs [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Share based compensation other than options grants in period			412,970		166,000		195,000
Granted in fiscal year, weighted average grant date fair value			$ 10.66		$ 11.20		$ 15.01
Equity instruments other than options, vested in period, total fair value			3,600,000		3,800,000		2,900,000
Unrecognized compensation expense			1,500,000
Unrecognized compensation expense recognized weighted average period			10 months 18 days
Equity instruments other than options, vested in period			287,168		435,169		376,819
Total intrinsic value of SAR's exercised			800,000		100,000		300,000
Non-Performance Based Restricted Stock Units (RSUs) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Share based compensation other than options grants in period			44,200		68,450		41,800
Granted in fiscal year, weighted average grant date fair value			$ 51.11		$ 47.10		$ 59.35
Unrecognized compensation expense			4,100,000
Unrecognized compensation expense recognized weighted average period			1 year 10 months 24 days
Equity instruments other than options, vested in period			0
Performance Based Restricted Stock Units (RSUs) [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Share based compensation other than options grants in period			255,604		0		0
Granted in fiscal year, weighted average grant date fair value			$ 49.51
Unrecognized compensation expense			7,900,000
Unrecognized compensation expense recognized weighted average period			1 year 6 months
Equity instruments other than options, vested in period			0
Exchange-Traded Futures Contracts [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Hedging collateral deposits			1,100,000		400,000
Amount Exceeds LIFO Basis [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gas stored underground - current			59,100,000
LIFO Method [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gas stored underground - current			$ 30,700,000

[1] Netting Adjustments represent the impact of legally-enforceable master netting arrangements that allow the Company to net gain and loss positions held with the same counterparties. The net asset or net liability for each counterparty is recorded as an asset or liability on the Company’s balance sheet. In the tables above, presenting asset and liability information by gas and oil positions may result in negative assets or negative liabilities in the Total column when a counterparty has issued both gas and oil swaps to the Company.