Capitalized Interest (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Rollforward of capitalized interest
Capitalized interest, beginning of period	$ 170.3	$ 190.0	$ 167.9	$ 191.2
Interest incurred	31.8	33.5	62.8	67.0
Interest charged to cost of sales	(32.0)	(37.3)	(60.6)	(72.0)
Capitalized interest, end of period	170.1	186.2	170.1	186.2
Financial Services [Member]
Rollforward of capitalized interest
Interest incurred	2.4	$ 1.8	4.5	$ 3.5
Forestar Group [Member]
Rollforward of capitalized interest
Interest incurred	$ 1.3		$ 1.4

Total interest costs incurred during the period and either capitalized or charged against earnings.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

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- Definition

Carrying amount as of the balance sheet date of interest costs that were capitalized to properties under development during the land development and construction period of a project, and which are included in inventory.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

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- Definition

Amount of interest cost charged to cost of sales that had been previously capitalized to inventory.

+ References

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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