Summary Of Significant Accounting Policies (Materials, Supplies and Emission Allowances (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Materials, Supplies and Emission Allowances [Line Items]
Materials and Supplies - at average cost	$ 34,880	$ 33,859
Emission Allowances	18,680	18,018
Materials, Supplies and Emission Allowances	$ 53,560	$ 51,877

Gross amount of unprocessed materials to be used in manufacturing or production process and supplies that will be consumed.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.6(a)(4),(5))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Name:	us-gaap_InventoryRawMaterialsAndSupplies
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant