The number of finished lots purchased through a business acquisition.

No definition available.

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- Definition

The number of homes acquired by the entity through a business acquisition.

+ References

No definition available.

+ Details

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- Definition

The number of lots the entity controls through option contracts as a result of a business acquisition.

+ References

No definition available.

+ Details

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- Definition

The sales order backlog (homes) acquired by the entity through a business acquisition.

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

Amount of direct costs of the business combination including legal, accounting, and other costs incurred to consummate the business acquisition.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Date when the business acquisition agreement was executed, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

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Period Type:	duration

- 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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Period Type:	duration

- Definition

Percentage of voting equity interests acquired at the acquisition date in the business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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Balance Type:	na
Period Type:	instant

- Definition

The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(2)-(3)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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Period Type:	duration

- Definition

The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(2)-(3)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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Period Type:	duration

- Definition

The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(2)-(3)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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- Definition

This element represents the fair value of the noncontrolling interest in the acquiree at the acquisition date.

+ References

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Period Type:	instant

- Definition

This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 23
-URI http://asc.fasb.org/extlink&oid=84229725&loc=d3e1043-128460

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- Definition

Amount of assets acquired at the acquisition date.

+ References

+ Details

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

- Definition

Amount of currency on hand as well as demand deposits with banks or financial institutions, acquired at the acquisition date. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

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

- Definition

Amount of liabilities incurred for goods and services received that are used in an entity's business and related party payables, assumed at the acquisition date.

+ References

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Amount of other liabilities due within one year or within the normal operating cycle, if longer, assumed at the acquisition date.

+ References

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

- Definition

Amount of assets, excluding financial assets and goodwill, that lack physical substance, having a projected indefinite period of benefit, acquired at the acquisition date.

+ References

+ Details

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

- Definition

The amount of inventory recognized as of the acquisition date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 55
-Paragraph 37
-URI http://asc.fasb.org/extlink&oid=84160947&loc=d3e2207-128464

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

- Definition

Amount of liabilities assumed at the acquisition date.

+ References

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

- Definition

Amount of long-term debt due after one year or the normal operating cycle, if longer, assumed at the acquisition date.

+ References

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

- Definition

Amount of other assets expected to be realized or consumed after one year or the normal operating cycle, if longer, acquired at the acquisition date.

+ References

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Period Type:	instant

- Definition

Amount recognized as of the acquisition date for the assets, including goodwill, in excess of (less than) the aggregate liabilities assumed, less the noncontrolling interest in the acquiree.

+ References

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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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Balance Type:	na
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- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

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- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

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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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Data Type:	xbrli:integerItemType
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Period Type:	instant

- Definition

The cash outflow associated with the acquisition of a business, net of the cash acquired from the purchase.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585

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Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Business Acquisitions (Details) $ / shares in Units, $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2018 USD ($) Market State $ / shares	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2016 USD ($)	Nov. 09, 2018 Lot Home	Oct. 05, 2017 USD ($)	Sep. 02, 2016 Lot Home
Business Acquisition [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired								75.00%
Payments to Acquire Businesses, Net of Cash Acquired				$ 159.2	$ 4.1	$ 82.2
Goodwill				109.2	80.0
Business Acquisition, Transaction Costs								$ 7.2
Business Combination, Acquisition Related Costs				5.3
Business Acquisition, Pro Forma Revenue				16,068.0	14,239.0
Business Acquisition, Pro Forma Net Income (Loss)				$ 1,463.6	$ 1,124.1
Business Acquisition, Pro Forma Earnings Per Share, Diluted \| $ / shares				$ 3.82	$ 2.97
Wilson Parker Homes [Member]
Business Acquisition [Line Items]
Business Acquisition, Date of Acquisition Agreement			Sep. 02, 2016
Payments to Acquire Businesses, Net of Cash Acquired			$ 91.9
Business Acquisition, Number of Homes Acquired \| Home									380
Business Acquisition, Number of Finished Lots Acquired \| Lot									490
Business Acquisition, Number of Lots Under Option Contracts \| Lot									1,850
Business Acquisition, Sales Order Backlog Acquired (Homes) \| Home									308
Goodwill, Acquired During Period			$ 0.0
Forestar Group [Member]
Business Acquisition [Line Items]
Business Acquisition, Date of Acquisition Agreement		Oct. 05, 2017
Payments to Acquire Businesses, Net of Cash Acquired		$ 558.3
Number Of Housing Construction Markets \| Market				24
Number of States in which Entity Operates \| State				14
Forestar Consolidated [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents								401.9
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory								334.6
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets								98.5
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets								51.6
Goodwill					$ 0.0			29.2
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets								915.8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable								2.8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other								49.4
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt								130.1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities								182.3
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value								175.2
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest								$ 558.3
Minimum [Member] \| Inventories [Member] \| Forestar Consolidated [Member]
Business Acquisition [Line Items]
Fair Value Inputs, Discount Rate		16.00%
Maximum [Member] \| Inventories [Member] \| Forestar Consolidated [Member]
Business Acquisition [Line Items]
Fair Value Inputs, Discount Rate		22.00%
Subsequent Event [Member] \| Westport Homes [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired	$ 190.0
Business Acquisition, Number of Homes Acquired \| Home							400
Business Acquisition, Number of Finished Lots Acquired \| Lot							3,500
Business Acquisition, Number of Lots Under Option Contracts \| Lot							3,200
Business Acquisition, Sales Order Backlog Acquired (Homes) \| Home							550