Summary of Significant Accounting Policies (Consolidated Statement of Cash Flows) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019		Sep. 30, 2018	Sep. 30, 2017
Cash and Cash Equivalents [Line Items]
Cash and Temporary Cash Investments	$ 20,541	$ 20,428		$ 229,606	$ 555,530
Hedging Collateral Deposits	0	6,832	[1]	3,441	1,741
Cash, Cash Equivalents and Restricted Cash	$ 20,541	$ 27,260		$ 233,047	$ 557,271

[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.