Regulatory Matters (Schedule Of Regulatory Assets And Liabilities) (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Sep. 30, 2015
Regulatory Assets And Liabilities [Line Items]
Total Regulatory Assets	[1]	$ 515,315	$ 469,097
Less: Amounts Included in Other Current Assets	[1]	(15,616)	(20,438)
Total Long-Term Regulatory Assets		320,750	278,227
Total Regulatory Liabilities		420,793	445,096
Less: Amounts Included in Current and Accrued Liabilities		(34,262)	(62,124)
Total Long-Term Regulatory Liabilities		99,789	108,617
Cost Of Removal Regulatory Liability [Member]
Regulatory Assets And Liabilities [Line Items]
Total Regulatory Liabilities		193,424	184,907
Taxes Refundable To Customers [Member]
Regulatory Assets And Liabilities [Line Items]
Total Regulatory Liabilities		93,318	89,448
Post-Retirement Benefit Costs [Member]
Regulatory Assets And Liabilities [Line Items]
Total Regulatory Liabilities		67,204	60,013
Amounts Payable To Customers [Member]
Regulatory Assets And Liabilities [Line Items]
Total Regulatory Liabilities		19,537	56,778
Off-System Sales And Capacity Release Credits [Member]
Regulatory Assets And Liabilities [Line Items]
Total Regulatory Liabilities		15,930	21,027
Other Accruals and Current Liabilities [Member]
Regulatory Assets And Liabilities [Line Items]
Less: Amounts Included in Current and Accrued Liabilities		(14,725)	(5,346)
Other Regulatory Liabilities [Member]
Regulatory Assets And Liabilities [Line Items]
Total Regulatory Liabilities	[2]	31,380	32,923
Total Long-Term Regulatory Liabilities		16,655	27,577
Non-Current Regulatory Liabilities [Member]
Regulatory Assets And Liabilities [Line Items]
Total Long-Term Regulatory Liabilities		386,531	382,972
Pension Costs Asset [Member]
Regulatory Assets And Liabilities [Line Items]
Total Regulatory Assets	[1],[3]	203,755	202,781
Post-Retirement Benefit Costs [Member]
Regulatory Assets And Liabilities [Line Items]
Total Regulatory Assets	[1],[3]	74,802	34,217
Recoverable Future Taxes [Member]
Regulatory Assets And Liabilities [Line Items]
Total Regulatory Assets	[1]	177,261	168,214
Environmental Site Remediation Costs [Member]
Regulatory Assets And Liabilities [Line Items]
Total Regulatory Assets	[1],[3]	23,392	24,606
NYPSC Assessment [Member]
Regulatory Assets And Liabilities [Line Items]
Total Regulatory Assets	[1],[4]	5,804	13,916
Asset Retirement Obligations [Member]
Regulatory Assets And Liabilities [Line Items]
Total Regulatory Assets	[1],[3]	12,490	12,250
Unamortized Debt Expense [Member]
Regulatory Assets And Liabilities [Line Items]
Total Regulatory Assets	[1]	1,688	2,218
Other Regulatory Assets [Member]
Regulatory Assets And Liabilities [Line Items]
Total Regulatory Assets	[1],[5]	16,123	10,895
Total Long-Term Regulatory Assets		6,311	4,373
Other Current Assets [Member]
Regulatory Assets And Liabilities [Line Items]
Less: Amounts Included in Other Current Assets		(9,812)	(6,522)
Long-Term Regulatory Assets [Member]
Regulatory Assets And Liabilities [Line Items]
Total Long-Term Regulatory Assets	[1]	$ 499,699	$ 448,659

[1] The Company recovers the cost of its regulatory assets but generally does not earn a return on them. There are a few exceptions to this rule. For example, the Company does earn a return on Unrecovered Purchased Gas Costs and, in the New York jurisdiction of its Utility segment, earns a return, within certain parameters, on the excess of cumulative funding to the pension plan over the cumulative amount collected in rates.

[2] $14,725 and $5,346 are included in Other Accruals and Current Liabilities on the Consolidated Balance Sheets at September 30, 2016 and 2015, respectively, since such amounts are expected to be recovered from ratepayers in the next 12 months. $16,655 and $27,577 are included in Other Regulatory Liabilities on the Consolidated Balance Sheets at September 30, 2016 and 2015, respectively.

[3] Included in Other Regulatory Assets on the Consolidated Balance Sheets.

[4] Amounts are included in Other Current Assets on the Consolidated Balance Sheets at September 30, 2016 and September 30, 2015 since such amounts are expected to be recovered from ratepayers in the next 12 months.

[5] $9,812 and $6,522 are included in Other Current Assets on the Consolidated Balance Sheets at September 30, 2016 and 2015, respectively, since such amounts are expected to be recovered from ratepayers in the next 12 months. $6,311 and $4,373 are included in Other Regulatory Assets on the Consolidated Balance Sheets at September 30, 2016 and 2015, respectively.