Valuation And Qualifying Accounts (Details) - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Valuation and Qualifying Accounts [Line Items]
Reversal of estimate for potential sequestration of AMT credit refunds			$ 5,000
Allowance for Uncollectible Accounts [Member]
Valuation and Qualifying Accounts [Line Items]
Balance at Beginning of Period		$ 25,788	24,537	$ 22,526
Additions Charged to Costs and Expenses		12,339	10,184	10,905
Additions Charged to Other Accounts	[1]	1,353	1,707	1,967
Deductions	[2]	16,670	10,640	10,861
Balance at End of Period		22,810	25,788	24,537
Valuation Allowance for Deferred Tax Assets [Member]
Valuation and Qualifying Accounts [Line Items]
Balance at Beginning of Period	[3]	0	5,000	0
Additions Charged to Costs and Expenses	[3]	63,205	0	5,000
Additions Charged to Other Accounts	[1],[3]	0	0	0
Deductions	[2],[3]	0	5,000	0
Balance at End of Period	[3]	$ 63,205	$ 0	$ 5,000

[1] Represents the discount on accounts receivable purchased in accordance with the Utility segment’s 2005 New York rate agreement.

[2] Amounts represent net accounts receivable written-off, as well as a reversal of a valuation allowance, as discussed in footnote (3) below.

[3] During fiscal 2020, a valuation allowance was recorded against certain state deferred tax assets. During fiscal 2019, there was a $5.0 million benefit recorded to reverse the valuation allowance established at September 30, 2018 related to the potential sequestration of estimated alternative minimum tax credit refunds as a result of the 2017 Tax Reform Act.