Fair Value Measurements - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Impairment of projects in process		$ 0	$ 110,000,000.0	$ 1,000,000.0
Impairment of land held for sale	$ 38,600,000	$ 1,300,000	$ 38,600,000	$ 5,900,000

The aggregate amount of write-downs for impairments recognized during the period for long-lived assets held for abandonment, exchange or sale.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2611-110228

Name:	us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration