Real Estate - Real Estate Table (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Real Estate Properties [Line Items]
Real estate	$ 1,309.7	$ 1,028.9
Land and Land Improvements [Member]
Real Estate Properties [Line Items]
Real estate	1,304.3	1,011.8
Land [Member]
Real Estate Properties [Line Items]
Real estate	$ 5.4	$ 17.1

Carrying amount as of the balance sheet date, net of valuation allowances and impairment losses, of costs of land expected to be developed in the near term plus capitalized costs of development, for purposes of selling completed units to home buyers or commercial or industrial entities..

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))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant