Segment Information - Narrative (Details) $ in Millions	3 Months Ended
Dec. 31, 2018 USD ($) Projects Market State Segments OperatingDivisions	Sep. 30, 2018 USD ($)
Segment Reporting Information [Line Items]
Multi-family property held for sale \| $		$ 0.0
Homebuilding [Member]
Segment Reporting Information [Line Items]
Number of housing construction markets \| Market	84
Number of housing construction states \| State	29
Number of home building operating divisions \| OperatingDivisions	51
Number of homebuilding reporting segments \| Segments	6
Forestar Group [Member]
Segment Reporting Information [Line Items]
Number of housing construction markets \| Market	35
Number of housing construction states \| State	16
Multifamily [Member] \| Other Segments [Member]
Segment Reporting Information [Line Items]
Property, Plant and Equipment, Gross \| $	$ 139.7	$ 171.4
Multi-family property held for sale \| $	$ 43.6
Asset under Construction [Member] \| Multifamily [Member] \| Other Segments [Member]
Segment Reporting Information [Line Items]
Number of Projects \| Projects	3
Assets Held-for-sale [Member] \| Multifamily [Member] \| Other Segments [Member]
Segment Reporting Information [Line Items]
Number of Projects \| Projects	1
Assets Leased to Others [Member] \| Multifamily [Member] \| Other Segments [Member]
Segment Reporting Information [Line Items]
Number of Projects \| Projects	3

The number of markets the entity operates in as of the balance sheet date.

No definition available.

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- Definition

Number of Projects

+ References

No definition available.

+ Details

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- Definition

Amount of other assets held-for-sale that are not part of a disposal group, expected to be sold within a year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 15
-Paragraph 4
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=77912953&loc=d3e400-110220

+ Details

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- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

+ References

No definition available.

+ Details

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- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

No definition available.

+ Details

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- Definition

The number of states the entity operates in as of the balance sheet date.

+ References

No definition available.

+ Details

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- Definition

Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.13)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Details

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