Asset Retirement Obligation (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Asset Retirement Obligation [Line Items]
Liabilities Incurred	$ 61,246	$ 4,122	$ 5,597
Shell Acquisition [Member]
Asset Retirement Obligation [Line Items]
Liabilities Incurred	$ 57,200

Amount of asset retirement obligations incurred during the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

Name:	us-gaap_AssetRetirementObligationLiabilitiesIncurred
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration