Forestar (FOR) 10-K 19 Nov 20 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Nov. 12, 2020	Mar. 31, 2020
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Sep. 30, 2020
Current Fiscal Year End Date	--09-30
Document Transition Report	false
Entity File Number	001-33662
Entity Registrant Name	Forestar Group Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-1336998
Entity Address, Address Line One	2221 E. Lamar Blvd.
Entity Address, Address Line Two	Suite 790
Entity Address, City or Town	Arlington
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	76006
City Area Code	817
Local Phone Number	769-1860
Title of 12(b) Security	Common Stock, par value $1.00 per share
Trading Symbol	FOR
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 190
Entity Common Stock, Shares Outstanding		48,070,347
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Central Index Key	0001406587

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
ASSETS
Cash and cash equivalents	$ 394.3	$ 382.8
Real estate	1,309.7	1,028.9
Investment in unconsolidated ventures	3.6	7.3
Income taxes receivable	6.3	3.2
Property and equipment, net	1.1	2.4
Deferred tax asset, net	0	17.4
Other assets	24.9	13.7
Total assets	1,739.9	1,455.7
LIABILITIES
Accounts payable	29.2	16.8
Earnest money on sales contracts	98.3	89.9
Deferred tax liability, net	5.7	0
Accrued expenses and other liabilities	93.8	79.6
Debt	641.1	460.5
Total liabilities	868.1	646.8
Commitments and Contingencies
Forestar Group Inc. shareholders’ equity:
Common stock, par value $1.00 per share, 200,000,000 authorized shares, 48,061,921 and 47,997,366 shares issued and outstanding at September 30, 2020 and 2019, respectively	$ 48.1	$ 48
Common stock, par value (in usd per share)	$ 1	$ 1
Common Stock, Shares Authorized	200,000,000	200,000,000
Common Stock, Shares, Issued	48,061,921	47,997,366
Additional paid-in capital	$ 603.9	$ 602.2
Retained earnings	218.9	158.1
Stockholders' equity	870.9	808.3
Noncontrolling interests	0.9	0.6
Total equity	871.8	808.9
Total liabilities and equity	$ 1,739.9	$ 1,455.7

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	3 Months Ended								9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenues	$ 347.6	$ 177.9	$ 159.1	$ 247.2	$ 236.3	$ 88.2	$ 65.3	$ 38.5	$ 78.3	$ 83.5	$ 931.8	$ 428.3
Cost of sales									49.5	90.1	813.7	362.7
Selling, general and administrative expense									19.4	51.2	45.7	28.9
Equity in earnings of unconsolidated ventures									(4.8)	(10.9)	(0.7)	(0.5)
Gain on sale of assets									(27.8)	(113.4)	(0.1)	(3)
Interest expense									3.7	6.4	0	0
Interest and other income									(6.4)	(2.4)	(4.9)	(5.5)
Income before income taxes	32	10.3	13.7	22.2	16	8.4	16.4	4.9	44.7	62.5	78.1	45.7
Income tax expense (benefit)	(7.5)	(0.2)	(3.3)	(5.4)	(3.4)	(1.5)	(3.6)	(1)	25.3	(33.4)	(16.4)	(9.4)
Net income	24.5	10.1	10.4	16.8	12.6	6.9	12.8	3.9	70	67.9	61.7	36.3
Net income attributable to noncontrolling interests	0.3	0	0.8	(0.1)	(0.1)	0	2.7	0.6	1.2	0.1	0.9	3.3
Net income attributable to Forestar Group Inc.	$ 24.2	$ 10.1	$ 9.6	$ 16.9	$ 12.7	$ 6.9	$ 10.1	$ 3.3	$ 68.8	$ 67.8	$ 60.8	$ 33
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Weighted average number of common shares									41,938,987	42,200,000	48,037,018	41,974,429
Adjusted weighted average number of common shares									41,969,056	42,500,000	48,094,111	42,005,141
Earnings Per Share, Basic [Abstract]
Basic net income per common share attributable to Forestar Group Inc.	$ 0.50	$ 0.21	$ 0.20	$ 0.35	$ 0.30	$ 0.16	$ 0.24	$ 0.08	$ 1.64	$ 1.61	$ 1.26	$ 0.79
Earnings Per Share, Diluted [Abstract]
Diluted net income per common share attributable to Forestar Group Inc.	$ 0.50	$ 0.21	$ 0.20	$ 0.35	$ 0.30	$ 0.16	$ 0.24	$ 0.08	$ 1.64	$ 1.59	$ 1.26	$ 0.79

CONSOLIDATED STATEMENTS OF EQUI

CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Noncontrolling Interest
Common Stock, Shares, Outstanding		41,938,936
Beginning Balances at Dec. 31, 2017	$ 605.6	$ 41.9	$ 506	$ 56.3	$ 1.4
Net income	70	0	0	68.8	1.2
Issuances of common stock, Value	0	0	0	0	0
Stock-based compensation expense	0.3	0	0.3	0	0
Distributions to noncontrolling interests	(1.4)	0	0	0	(1.4)
Issuance of common stock	0
Ending Balances at Sep. 30, 2018	674.5	$ 41.9	506.3	125.1	1.2
Issuances of common stock under employee benefit plans, Shares		(467)
Common Stock, Shares, Outstanding		41,939,403
Net income	36.3	$ 0	0	33	3.3
Issuances of common stock, Value	0	(0.1)	(0.1)	0	0
Stock-based compensation expense	1.3	0	1.3	0	0
Distributions to noncontrolling interests	(3.9)	0	0	0	(3.9)
Issuance of common stock	100.7	6	94.7	0	0
Ending Balances at Sep. 30, 2019	808.9	$ 48	602.2	158.1	0.6
Issuances of common stock under employee benefit plans, Shares		(20,463)
Shares Issued During Period, New Issues		6,037,500
Common Stock, Shares, Outstanding		47,997,366
Net income	61.7	$ 0	0	60.8	0.9
Issuances of common stock, Value	(0.1)	(0.1)	0	0	0
Shares withheld for payroll taxes, Value	(0.3)	0	(0.3)	0	0
Stock-based compensation expense	2	0	2	0	0
Distributions to noncontrolling interests	(0.6)	0	0	0	(0.6)
Issuance of common stock	0
Ending Balances at Sep. 30, 2020	$ 871.8	$ 48.1	$ 603.9	$ 218.9	$ 0.9
Issuances of common stock under employee benefit plans, Shares		(64,555)
Common Stock, Shares, Outstanding		48,061,921

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)
OPERATING ACTIVITIES
Net income	$ 70	$ 61.7	$ 36.3
Adjustments:
Depreciation and amortization	3.9	4.9	6.7
Deferred income taxes	(24.8)	23.1	9.5
Equity in earnings of unconsolidated ventures	(4.8)	(0.7)	(0.5)
Distributions of earnings of unconsolidated ventures	3.5	0	4.9
Stock-based compensation expense	0.3	2	1.3
Real estate and land option charges	0.3	0.9	1.3
Gain on sale of assets	27.8	0.1	3
Other	(0.9)	(0.1)	(0.1)
Changes in operating assets and liabilities:
Increase in real estate	(361.1)	(281.7)	(531.7)
(Increase) decrease in other assets	(1.6)	(3.4)	0.3
Increase in accounts payable and other accrued liabilities	18.4	24	41.9
Increase in earnest money deposits on sales contracts	37.5	3.9	40.5
(Increase) decrease in income taxes receivable	2.3	(3.1)	1.2
Net cash used in operating activities	283	(168.4)	391.2
INVESTING ACTIVITIES
Expenditures for property, equipment, software and other	(0.1)	(0.6)	(0.9)
Return of investment in unconsolidated ventures	0.8	4.3	0.1
Proceeds from sale of assets	258.3	1.3	0
Net cash provided by (used in) investing activities	259	5	(0.8)
FINANCING ACTIVITIES
Issuance of common stock	0	0	100.7
Proceeds from debt	0.2	300	435
Repayments of debt	(0.5)	(118.9)	(85)
Deferred financing fees	(2.3)	(5.3)	(6.9)
Distributions to noncontrolling interests, net	(1.4)	(0.6)	(3.9)
Cash paid for shares withheld for taxes	0	(0.3)	(0.1)
Net cash provided by (used in) financing activities	(4)	174.9	439.8
Net increase (decrease) in cash and cash equivalents	(28)	11.5	47.8
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	335	394.3	382.8
Cash paid during the year for:
Interest paid, net of amounts capitalized	0.9	0	0
Income taxes refunded, net	$ (3.4)	$ (3.1)	$ (1.7)

Transition Period Comparative D

Transition Period Comparative Data (Notes)	12 Months Ended
	Sep. 30, 2020
Transition Period Comparative Data [Abstract]
Transition Period Comparative Disclosures [Text Block]	Transition Period Comparative Data The following table presents certain financial information for the nine months ended September 30, 2018 and 2017 (in millions, except per share amounts). For the Nine Months Ended September 30, 2018 2017 (Unaudited) Revenues $ 78.3 $ 83.5 Cost of sales 49.5 90.1 Selling, general and administrative expense 19.4 51.2 Equity in earnings of unconsolidated ventures (4.8) (10.9) Gain on sale of assets (27.8) (113.4) Interest expense 3.7 6.4 Interest and other income (6.4) (2.4) Income from continuing operations before taxes 44.7 62.5 Income tax (benefit) expense (25.3) 33.4 Net income from continuing operations 70.0 29.1 Income from discontinued operations, net of taxes — 38.8 Net income 70.0 67.9 Net income attributable to noncontrolling interests 1.2 0.1 Net income attributable to Forestar Group Inc. $ 68.8 $ 67.8 Weighted Average Common Shares Outstanding: Basic 41.9 42.2 Diluted 42.0 42.5 Net Income per Basic Share: Continuing operations $ 1.64 $ 0.69 Discontinued operations $ — $ 0.92 Net income per basic share $ 1.64 $ 1.61 Net Income per Diluted Share: Continuing operations $ 1.64 $ 0.68 Discontinued operations $ — $ 0.91 Net income per diluted share $ 1.64 $ 1.59

Transition Period Comparative_2

Transition Period Comparative Data (Tables)	12 Months Ended
	Sep. 30, 2020
Transition Period Comparative Data [Abstract]
Transition Period Comparative Data Table Text Block [Table Text Block]	The following table presents certain financial information for the nine months ended September 30, 2018 and 2017 (in millions, except per share amounts). For the Nine Months Ended September 30, 2018 2017 (Unaudited) Revenues $ 78.3 $ 83.5 Cost of sales 49.5 90.1 Selling, general and administrative expense 19.4 51.2 Equity in earnings of unconsolidated ventures (4.8) (10.9) Gain on sale of assets (27.8) (113.4) Interest expense 3.7 6.4 Interest and other income (6.4) (2.4) Income from continuing operations before taxes 44.7 62.5 Income tax (benefit) expense (25.3) 33.4 Net income from continuing operations 70.0 29.1 Income from discontinued operations, net of taxes — 38.8 Net income 70.0 67.9 Net income attributable to noncontrolling interests 1.2 0.1 Net income attributable to Forestar Group Inc. $ 68.8 $ 67.8 Weighted Average Common Shares Outstanding: Basic 41.9 42.2 Diluted 42.0 42.5 Net Income per Basic Share: Continuing operations $ 1.64 $ 0.69 Discontinued operations $ — $ 0.92 Net income per basic share $ 1.64 $ 1.61 Net Income per Diluted Share: Continuing operations $ 1.64 $ 0.68 Discontinued operations $ — $ 0.91 Net income per diluted share $ 1.64 $ 1.59

Transition Period Comparative_3

Transition Period Comparative Data (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Transition Period Comparative Data [Abstract]
Total revenues	$ 78.3	$ 83.5
Cost of sales	49.5	90.1
Selling, general and administrative expense	19.4	51.2
Equity in earnings of unconsolidated ventures	(4.8)	(10.9)
Gain on sale of assets	(27.8)	(113.4)
Interest expense	3.7	6.4
Interest and other income	6.4	2.4
Income before income taxes	44.7	62.5
Income tax expense (benefit)	25.3	(33.4)
Net income from continuing operations	70	29.1
Income from discontinued operations, net of taxes	0	38.8
Net income	70	67.9
Net income attributable to noncontrolling interests	1.2	0.1
Net income attributable to Forestar Group Inc.	$ 68.8	$ 67.8
Weighted average number of common shares	41,938,987	42,200,000
Adjusted weighted average number of common shares	41,969,056	42,500,000
Continuing operations, basic (usd per share)	$ 1.64	$ 0.69
Discontinued operations, basic (usd per share)	0	0.92
Basic net income per common share attributable to Forestar Group Inc.	1.64	1.61
Continuing operations, diluted (usd per share)	1.64	0.68
Discontinued operations, diluted (usd per share)	0	0.91
Diluted net income per common share attributable to Forestar Group Inc.	$ 1.64	$ 1.59

Accounting Policies

Accounting Policies	12 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with U.S. Generally Accepted Accounting Principles (GAAP) and include the accounts of Forestar Group Inc. (Forestar) and all of its 100% owned, majority-owned and controlled subsidiaries, which are collectively referred to as the Company unless the context otherwise requires. The Company accounts for its investment in other entities in which it has significant influence over operations and financial policies using the equity method. All intercompany accounts, transactions and balances have been eliminated in consolidation. Noncontrolling interests in consolidated pass-through entities are recognized before income taxes. The transactions included in net income in the consolidated statements of operations are the same as those that would be presented in comprehensive income. Thus, the Company's net income equates to comprehensive income. In October 2017, Forestar became a majority-owned subsidiary of D.R. Horton, Inc. (D.R. Horton) by virtue of a merger with a wholly-owned subsidiary of D.R. Horton. Immediately following the merger, D.R. Horton owned 75% of the Company's outstanding common stock. In connection with the merger, the Company entered into certain agreements with D.R. Horton including a Stockholder’s Agreement, a Master Supply Agreement and a Shared Services Agreement. D.R. Horton is considered a related party of Forestar under GAAP. At September 30, 2020, D.R. Horton owned approximately 65% of the Company's outstanding common stock. Change in Fiscal Year Following the merger with D.R. Horton, the Company changed its fiscal year-end from December 31 to September 30, effective January 1, 2018. This change aligned Forestar's fiscal year-end reporting calendar with D.R. Horton. The Company's results of operations, cash flows and all transactions impacting stockholders' equity presented in this Form 10-K are for the fiscal years ended September 30, 2020 and 2019 and for the nine months ended September 30, 2018 unless otherwise noted. This Form 10-K also includes an unaudited statement of operations for the comparable stub period of January 1, 2017 to September 30, 2017. See Note 17. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions. These estimates and assumptions affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ materially from those estimates. Strategic Asset Sale In February 2018, the Company entered into and closed on a Purchase and Sale Agreement with Starwood Land, L.P. (Starwood) to sell 24 legacy projects for $232.0 million which generated $217.5 million in net proceeds. This strategic asset sale included projects owned both directly and indirectly through ventures and consisted of approximately 750 developed and under development lots, over 4,000 future undeveloped lots, 730 unentitled acres in California, an interest in one multi-family operating property and a multi-family development site. Adoption of New Accounting Standard In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-02, “Leases,” which requires that lease assets and liabilities be recognized on the balance sheet and that key information about leasing arrangements be disclosed. The guidance was effective for the Company beginning October 1, 2019 and did not have a material impact on its consolidated financial position, results of operations or cash flows. As a result of the adoption of this standard on October 1, 2019, the Company recorded right of use assets of $2.7 million and lease liabilities of $2.9 million. Lease right of use assets are included in other assets and lease liabilities are included in accrued expenses and other liabilities in the consolidated balance sheet. Revenue Recognition Real estate revenue and related profit are generally recognized at the time of the closing of a sale, when title to and possession of the property are transferred to the buyer. The Company’s performance obligation, to deliver the agreed-upon land or lots, is generally satisfied at closing. However, there may be instances in which the Company has an unsatisfied remaining performance obligation at the time of closing. In these instances, the Company records contract liabilities and recognizes those revenues over time as the performance obligations are completed. Generally, the Company's unsatisfied remaining performance obligations are expected to have an original duration of less than one year. See Note 4. Cash and Cash Equivalents Cash and cash equivalents include cash, other short-term instruments with original maturities of three months or less and proceeds from land and lot closings held for the Company’s benefit at title companies. Real Estate and Cost of Sales Real estate includes the costs of direct land and lot acquisition, land development, capitalized interest, and direct overhead costs incurred during land development. All indirect overhead costs, such as compensation of management personnel and insurance costs, are charged to selling, general and administrative expense as incurred. Land and development costs are typically allocated to individual residential lots based on the relative sales value of the lot. Cost of sales includes applicable land and lot acquisition, land development and related costs (both incurred and estimated to be incurred) allocated to each residential lot in the project. Any changes to the estimated total development costs subsequent to the initial lot sales are generally allocated to the remaining lots. The Company receives earnest money deposits from homebuilders for purchases of developed lots. These earnest money deposits are typically released to the homebuilders as lots are sold. Earnest money deposits from D.R. Horton are subject to mortgages which are secured by the real estate under contract with D.R. Horton. These mortgages expire when the earnest money is released to D.R. Horton as lots are sold. See Note 15 for related party transactions and balances. The Company has agreements with certain utility or improvement districts to convey water, sewer and other infrastructure-related assets it has constructed in connection with projects within their jurisdiction and receive reimbursements for the cost of these improvements. The reimbursement amounts for these improvements are defined by the district and are based on the allowable costs of the improvements. The transfer is consummated and the Company generally receives payment when the districts have a sufficient tax base to support funding of their bonds. The cost incurred by the Company in constructing these improvements, net of the amount expected to be collected in the future, is included in the Company's land development budgets and in the determination of lot costs. The Company reviews real estate assets held for use for impairment when events or circumstances indicate that their carrying value may not be recoverable. Impairment exists if the carrying amount of the asset is not recoverable from the undiscounted cash flows expected from its use and eventual disposition. The amount of the impairment loss is determined by comparing the carrying value of the asset to its estimated fair value, which is generally determined based on the present value of future cash flows expected from the sale of the asset. Real estate impairments are included in cost of sales in the consolidated statements of operations. See Note 3. Capitalized Interest The Company capitalizes interest costs throughout the development period (active real estate). Capitalized interest is charged to cost of sales as the related real estate is sold to the buyer. During periods in which the Company’s active real estate is lower than its debt level, a portion of the interest incurred is reflected as interest expense in the period incurred. During fiscal 2020 and 2019, the Company’s active real estate exceeded its debt level, and all interest incurred was capitalized to real estate. See Note 5. Property and Equipment Property and equipment are stated at cost less accumulated depreciation. The cost of significant additions and improvements is capitalized and the cost of repairs and maintenance is expensed as incurred. Depreciation generally is recorded using the straight-line method over the estimated useful life of the asset as follows: Estimated Useful Lives September 30, 2020 2019 (In millions) Leasehold improvements 5 to 10 years $ 1.2 $ 0.9 Property and equipment 2 to 10 years 1.1 3.4 Total property and equipment 2.3 4.3 Accumulated depreciation (1.2) (1.9) Property and equipment, net $ 1.1 $ 2.4 Depreciation expense was $0.3 million, $0.3 million and $0.2 million in fiscal 2020, 2019 and the nine months ended September 30, 2018, respectively. Income Taxes The Company’s income tax expense is calculated using the asset and liability method, under which deferred tax assets and liabilities are recognized based on the future tax consequences attributable to temporary differences between the financial statement amounts of assets and liabilities and their respective tax bases and attributable to net operating losses and tax credit carryforwards. When assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some portion or all of its deferred tax assets will not be realized. The realization of deferred tax assets is dependent upon the generation of sufficient taxable income in future periods and in the jurisdictions in which those temporary differences become deductible. The Company records a valuation allowance when it determines it is more likely than not that a portion of the deferred tax assets will not be realized. The accounting for deferred taxes is based upon estimates of future results. Differences between the anticipated and actual outcomes of these future results could have a material impact on the Company’s consolidated results of operations or financial position. Also, changes in existing federal and state tax laws and tax rates could affect future tax results and the valuation of the Company’s deferred tax assets and liabilities. Interest and penalties related to unrecognized tax benefits are recognized in the financial statements as a component of income tax expense. Significant judgment is required to evaluate uncertain tax positions. The Company evaluates its uncertain tax positions on a quarterly basis. The evaluations are based upon a number of factors, including changes in facts or circumstances, changes in tax law, correspondence with tax authorities during the course of audits and effective settlement of audit issues. Changes in the recognition or measurement of uncertain tax positions could result in increases or decreases in the Company’s income tax expense in the period in which the change is made. See Note 11. Stock-Based Compensation The Company’s stockholders formally authorize shares of its common stock to be available for future grants of stock-based compensation awards. From time to time, the Compensation Committee of the Company’s Board of Directors authorizes the grant of stock-based compensation to its employees and directors from these available shares. At September 30, 2020, the outstanding stock-based compensation awards consist of restricted stock units. Grants of restricted stock units vest over a certain number of years as determined by the Compensation Committee of the Board of Directors. Restricted stock units outstanding at September 30, 2020 have a remaining vesting period of 1 to 5 years. The compensation expense for stock-based awards is based on the fair value of the award and is recognized on a straight-line basis over the remaining vesting period. The fair values of restricted stock units are based on the Company’s stock price at the date of grant. See Note 13. Fair Value Measurements The FASB's authoritative guidance for fair value measurements establishes a three-level hierarchy based upon the inputs to the valuation model of an asset or liability. When available, the Company uses quoted market prices in active markets to determine fair value. Non-financial assets measured at fair value on a non-recurring basis principally include real estate assets which the Company reviews for indicators of impairment when events and circumstances indicate that the carrying value is not recoverable. See Note 9. Pending Accounting Standards In June 2016, the FASB issued ASU 2016-13, “Financial Instruments - Credit Losses,” which replaces the current incurred loss impairment methodology with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information in determining credit loss estimates. The guidance is effective for the Company beginning October 1, 2020 and is not expected to have a material impact on its consolidated financial position, results of operations or cash flows. In December 2019, the FASB issued ASU 2019-12 related to simplifying the accounting for income taxes. The guidance is effective for the Company beginning October 1, 2021, although early adoption is permitted. The Company is currently evaluating the impact of this guidance, and it is not expected to have a material impact on its consolidated financial position, results of operations or cash flows. In March 2020, the FASB issued ASU 2020-04, “Reference Rate Reform,” which provides optional expedients and exceptions for applying U.S. GAAP to contracts, hedging relationships, and other transactions affected by the discontinuation of the London Interbank Offered Rate (LIBOR) or by another reference rate expected to be discontinued. The guidance was effective beginning March 12, 2020 and can be applied prospectively through December 31, 2022. The Company will adopt this standard when LIBOR is discontinued and does not expect it to have a material impact on its consolidated financial statements and related disclosures.

Segment Information

Segment Information	12 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Segment Information	Segment Information Since the beginning of fiscal 2019, the Company has managed its operations through its real estate segment, which is its core business and generates substantially all of its revenues. The real estate segment primarily acquires land and develops infrastructure for single-family residential communities, and its revenues generally come from sales of residential single-family finished lots to local, regional and national homebuilders. The Company has other business activities for which the related assets and operating results are immaterial, and therefore are included within the Company's real estate segment. As such, the operating results of the Company's real estate segment are consistent with its consolidated operating results and no separate disclosure is required as of and for the fiscal years ended September 30, 2020 and 2019. During the nine months ended September 30, 2018, the Company managed its operations through its real estate segment and other segment (previously referred to as other natural resources). Additionally, certain costs and assets were not allocated to the Company’s segments. The accounting policies of the segments are the same as those described throughout Note 1. Segment results for the nine months ended September 30, 2018 were as follows: Nine Months Ended September 30, 2018 Real Estate Other Items Not Allocated Consolidated (In millions) Revenues $ 78.3 $ — $ — $ 78.3 Cost of sales 48.9 0.6 — 49.5 Selling, general and administrative expense 7.1 0.3 12.0 19.4 Equity in earnings of unconsolidated ventures (4.8) — — (4.8) Gain on sale of assets (1) (18.6) (9.2) — (27.8) Interest expense — — 3.7 3.7 Interest and other income (1.8) — (4.6) (6.4) Income before income taxes 47.5 8.3 (11.1) 44.7 Net income attributable to noncontrolling interests 1.2 — — 1.2 Income before income taxes attributable to Forestar Group Inc. $ 46.3 $ 8.3 $ (11.1) $ 43.5 ______________ (1) Gain on sale of ass ets within the real estate segment consisted primarily of a gain of $14.6 million related to the sale of the Company's interest in a multi-family venture near Denver. Gain on sale of assets within the other segment relates to the sale of non-core water interests in Texas, Louisiana, Georgia and Alabama.

Real Estate

Real Estate	12 Months Ended
	Sep. 30, 2020
Real Estate [Abstract]
Real Estate	Real Estate Real estate consists of: September 30, 2020 2019 (In millions) Developed and under development projects $ 1,304.3 $ 1,011.8 Undeveloped land 5.4 17.1 $ 1,309.7 $ 1,028.9 In fiscal 2020, the Company invested $550.8 million for the acquisition of residential real estate and $503.0 million for the development of residential real estate. At September 30, 2020 and 2019, undeveloped land primarily consists of undeveloped land which the Company has the contractual right to sell to D.R. Horton within approximately one year of its purchase or, if D.R. Horton elects, at an earlier date, at a sales price equal to the carrying value of the land at the time of sale plus additional consideration of 16% per annum. Each quarter the Company reviews the performance and outlook for all of its real estate for indicators of potential impairment and performs detailed impairment evaluations and analyses when necessary. As a result of this process there were no real estate impairment charges recorded in fiscal 2020 and $0.8 million and $0.3 million of impairment charges were recorded during fiscal 2019 and the nine months ended September 30, 2018, respectively. During fiscal 2020 and 2019, pre-acquisition cost write-offs related to land purchase contracts that the Company has terminated or expects to terminate were $0.9 million and $0.2 million, respectively. There were no pre-acquisition cost write-offs in the nine months ended September 30, 2018. Real estate impairments and land option charges are included in cost of sales in the consolidated statements of operations.

Revenue (Notes)

Revenue (Notes)	12 Months Ended
	Sep. 30, 2020
Revenues [Abstract]
Revenue from Contract with Customer [Text Block]	Revenues Revenues consist of: Year Ended September 30, Nine Months Ended 2020 2019 (In millions) Residential lot sales $ 880.3 $ 351.7 $ 72.0 Residential tract sales 48.6 55.8 3.6 Commercial tract sales 2.5 18.5 2.0 Other 0.4 2.3 0.7 $ 931.8 $ 428.3 $ 78.3 Land and lot sales to D.R. Horton were $887.6 million, $326.6 million and $39.1 million in fiscal 2020, 2019 and the nine months ended September 30, 2018, respectively.

Capitalized Interest

Capitalized Interest	12 Months Ended
	Sep. 30, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Capitalized Interest	Capitalized Interest The following table summarizes the Company’s interest costs incurred, capitalized and expensed in fiscal 2020, 2019 and the nine months ended September 30, 2018. Year Ended September 30, Nine Months Ended 2020 2019 (In millions) Capitalized interest, beginning of period $ 23.7 $ 3.2 $ 0.5 Interest incurred 43.3 25.3 7.3 Interest expensed: Directly to interest expense — — (3.7) Charged to cost of sales (18.3) (4.8) (0.9) Capitalized interest, end of period $ 48.7 $ 23.7 $ 3.2

Investments, Equity Method and

Investments, Equity Method and Joint Ventures	12 Months Ended
	Sep. 30, 2020
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investments and Joint Ventures Disclosure	Investment in Unconsolidated Ventures In the past, the Company has participated in real estate ventures for the purpose of acquiring and developing residential, multi-family and mixed-use communities in which it may or may not have a controlling financial interest. GAAP requires consolidation of variable interest entities (VIEs) in which an enterprise has a controlling financial interest and is the primary beneficiary. A controlling financial interest will have both of the following characteristics: (a) the power to direct the VIE activities that most significantly impact economic performance and (b) the obligation to absorb the VIE losses and right to receive benefits that are significant to the VIE. The Company examines specific criteria and uses judgment when determining whether a venture is a VIE and whether it is the primary beneficiary. The Company performs this review initially at the time it enters into venture agreements and reassesses upon reconsideration events. At September 30, 2020, the Company had ownership interests in four ventures that it accounted for using the equity method. Combined summarized balance sheet and income statement information for these unconsolidated ventures follows: September 30, 2020 2019 (In millions) Assets: Cash and cash equivalents $ 1.2 $ 1.6 Real estate 6.1 13.6 Other assets 0.2 0.1 Total assets $ 7.5 $ 15.3 Liabilities and Equity: Accounts payable and other liabilities $ 0.2 $ 0.3 Equity 7.3 15.0 Total liabilities and equity $ 7.5 $ 15.3 Forestar's investment in unconsolidated ventures $ 3.6 $ 7.3 Year Ended September 30, Nine Months Ended 2020 2019 (In millions) Revenues $ 3.5 $ 1.9 $ 22.2 Earnings 3.8 1.3 15.1 Forestar's equity in earnings of unconsolidated ventures 0.7 0.5 4.8 During fiscal 2020, 2019 and the nine months ended September 30, 2018, the Company made no further investments in these ventures and received $4.3 million, $5.0 million and $4.3 million, respectively, in distributions. Distributions include both return of investments and distributions of earnings. In the nine months ended September 30, 2018, the Company's equity in earnings from one of its unconsolidated ventures in which it owns a 37.5% interest, LM Land Holdings, LP, accounted for over 10% of the Company's consolidated pre-tax income. At September 30, 2018, LM Land Holdings, LP had $21.6 million in venture assets, $0.4 million in accounts payable and other liabilities, and $21.2 million in venture equity on its balance sheet. At September 30, 2018, the Company's investment in this venture was $8.9 million. In the nine months ended September 30, 2018, LM Land Holdings, LP recognized $17.4 million of revenues and generated $18.1 million in earnings, which includes $5.7 million of earnings related to the recognition of a deferred gain. The Company's share of these earnings was $6.4 million.

Other Assets, Accrued Expenses

Other Assets, Accrued Expenses and Other Liabilities (Notes)	12 Months Ended
	Sep. 30, 2020
Other Assets, Accrued Expenses and Other Liabilities [Abstract]
Other Assets And Other Liabilities [Text Block]	Other Assets, Accrued Expenses and Other Liabilities The Company's other assets at September 30, 2020 and 2019 were as follows: September 30, 2020 2019 (In millions) Receivables, net $ 0.4 $ 1.1 Earnest money notes receivable on sales contracts 4.8 — Lease right of use assets 3.6 — Prepaid expenses 4.9 3.4 Land purchase contract deposits 5.5 5.1 Other assets 5.7 4.1 $ 24.9 $ 13.7 The Company's accrued expenses and other liabilities at September 30, 2020 and 2019 were as follows: September 30, 2020 2019 (In millions) Accrued employee compensation and benefits $ 6.2 $ 5.6 Accrued property taxes 3.8 2.1 Lease liabilities 3.8 — Accrued interest 14.0 13.5 Contract liabilities 0.2 2.5 Deferred income 9.3 9.3 State income taxes payable 0.5 — Accrued development costs 35.3 35.4 Other accrued expenses 10.2 8.4 Other liabilities 10.5 2.8 $ 93.8 $ 79.6

Debt

Debt	12 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Debt	Debt The Company's notes payable at their carrying amounts consist of the following: September 30, 2020 2019 (In millions) Unsecured: 3.75% convertible senior notes due 2020 $ — $ 116.7 8.0% senior notes due 2024 (1) 345.2 343.8 5.0% senior notes due 2028 (1) 295.9 — Revolving credit facility — — $ 641.1 $ 460.5 ______________ (1) Unamortized debt issuance costs that were deducted from the carrying amounts of the senior notes totaled $8.9 million and $6.2 million at September 30, 2020 and 2019, respectively. Bank Credit Facility The Company has a $380 million senior unsecured revolving credit facility with an uncommitted accordion feature that could increase the size of the facility to $570 million, subject to certain conditions and availability of additional bank commitments. The facility also provides for the issuance of letters of credit with a sublimit equal to the greater of $100 million and 50% of the revolving credit commitment. Borrowings under the revolving credit facility are subject to a borrowing base calculation based on the book value of the Company's real estate assets and unrestricted cash. Letters of credit issued under the facility reduce the available borrowing capacity. There were no borrowings or repayments under the facility during fiscal 2020. At September 30, 2020, there were no borrowings outstanding and $36.0 million of letters of credit issued under the revolving credit facility, resulting in available capacity of $344.0 million. The maturity date of the facility is October 2, 2022, which can be extended by up to one year on up to two additional occasions, subject to the approval of lenders holding a majority of the commitments. The revolving credit facility includes customary affirmative and negative covenants, events of default and financial covenants. The financial covenants require a minimum level of tangible net worth, a minimum level of liquidity and a maximum allowable leverage ratio. These covenants are measured as defined in the credit agreement governing the facility and are reported to the lenders quarterly. A failure to comply with these financial covenants could allow the lending banks to terminate the availability of funds under the revolving credit facility or cause any outstanding borrowings to become due and payable prior to maturity. At September 30, 2020, the Company was in compliance with all of the covenants, limitations and restrictions of its revolving credit facility. Senior Notes In February 2020, the Company issued $300 million principal amount of 5.0% senior notes pursuant to Rule 144A and Regulation S under the Securities Act of 1933, as amended. The notes mature March 1, 2028 with interest payable semi-annually and represent senior unsecured obligations that rank equally in right of payment to all existing and future senior unsecured indebtedness. The notes may be redeemed prior to maturity, subject to certain limitations and premiums defined in the indenture agreement. On or after March 1, 2023, the notes may be redeemed at 102.5% of their principal amount plus any accrued and unpaid interest. In accordance with the indenture, the redemption price decreases annually thereafter and the notes can be redeemed at par on or after March 1, 2026 through maturity. The notes are guaranteed by each of the Company's subsidiaries to the extent such subsidiaries guarantee the Company's revolving credit facility. The annual effective interest rate of the notes after giving effect to the amortization of financing costs is 5.2%. The Company also has $350 million principal amount of 8.0% senior notes outstanding. The notes mature April 15, 2024 with interest payable semi-annually and represent senior unsecured obligations that rank equally in right of payment to all existing and future senior unsecured indebtedness. The notes may be redeemed prior to maturity, subject to certain limitations and premiums defined in the indenture agreement. On or after April 15, 2021, the notes may be redeemed at 104% of their principal amount plus any accrued and unpaid interest. In accordance with the indenture, the redemption price decreases annually thereafter and the notes can be redeemed at par on or after April 15, 2023 through maturity. The notes are guaranteed by each of the Company's subsidiaries to the extent such subsidiaries guarantee the Company's revolving credit facility. The annual effective interest rate of the notes after giving effect to the amortization of financing costs is 8.5%. In March 2020, the Company repaid $118.9 million principal amount of its 3.75% convertible senior notes in cash at maturity. The indentures governing the senior notes require that, upon the occurrence of both a change of control and a rating decline (each as defined in the indentures), the Company offer to purchase the notes at 101% of their principal amount. If the Company or its restricted subsidiaries dispose of assets, under certain circumstances, the Company will be required to either invest the net cash proceeds from such asset sales in its business within a specified period of time, repay certain senior secured debt or debt of its non-guarantor subsidiaries, or make an offer to purchase a principal amount of the notes equal to the excess net cash proceeds at a purchase price of 100% of their principal amount. The indentures contain covenants that, among other things, restrict the ability of the Company and its restricted subsidiaries to pay dividends or distributions, repurchase equity, prepay subordinated debt and make certain investments; incur additional debt or issue mandatorily redeemable equity; incur liens on assets; merge or consolidate with another company or sell or otherwise dispose of all or substantially all of the Company’s assets; enter into transactions with affiliates; and allow to exist certain restrictions on the ability of subsidiaries to pay dividends or make other payments. At September 30, 2020, the Company was in compliance with all of the limitations and restrictions associated with its senior note obligations. Effective April 30, 2020, the Board of Directors authorized the repurchase of up to $30 million of the Company’s debt securities. The authorization has no expiration date. All of the $30 million authorization was remaining at September 30, 2020.

Fair Value

Fair Value	12 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value	Fair Value Measurements Fair value is the exchange price that would be received for an asset or paid to transfer a liability in an orderly transaction between market participants. In arriving at a fair value measurement, the Company uses a fair value hierarchy based on three levels of inputs, of which the first two are considered observable and the last unobservable. The three levels of inputs used to establish fair value are the following: • Level 1 — Quoted prices in active markets for identical assets or liabilities; • Level 2 — Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and • Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. The Company elected not to use the fair value option for cash and cash equivalents and debt. For the financial assets and liabilities that the Company does not reflect at fair value, the following tables present both their respective carrying value and fair value at September 30, 2020 and 2019. Fair Value at September 30, 2020 Carrying Value Level 1 Level 2 Level 3 Total (in millions) Cash and cash equivalents (a) $ 394.3 $ 394.3 $ — $ — $ 394.3 Debt (b) 641.1 — 673.5 — 673.5 Fair Value at September 30, 2019 Carrying Value Level 1 Level 2 Level 3 Total (in millions) Cash and cash equivalents (a) $ 382.8 $ 382.8 $ — $ — $ 382.8 Debt (b) 460.5 — 497.3 — 497.3 _____________________ (a) The fair values of cash and cash equivalents approximate their carrying values due to their short-term nature and are classified as Level 1 within the fair value hierarchy. (b) At September 30, 2020 and 2019, debt consisted of the Company's senior notes. The fair value of the senior notes is determined based on quoted market prices, which is classified as Level 2 within the fair value hierarchy. Non-financial assets measured at fair value on a non-recurring basis primarily include real estate assets which the Company reviews for indicators of potential impairment and performs impairment evaluations when necessary.

Earnings Per Share

Earnings Per Share	12 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Earnings Per Share	Earnings per Share The computations of basic and diluted earnings per share are as follows: Year Ended September 30, Nine Months Ended 2020 2019 (In millions, except share and per share amounts) Numerator: Net income attributable to Forestar Group Inc. $ 60.8 $ 33.0 $ 68.8 Denominator: Weighted average common shares outstanding — basic 48,037,018 41,974,429 41,938,987 Dilutive effect of stock-based compensation 57,093 30,712 30,069 Total weighted average shares outstanding — diluted 48,094,111 42,005,141 41,969,056 Basic net income per common share attributable to Forestar Group Inc. $ 1.26 $ 0.79 $ 1.64 Diluted net income per common share attributable to Forestar Group Inc. $ 1.26 $ 0.79 $ 1.64 In March 2020, the Company repaid $118.9 million principal amount of its 3.75% convertible senior notes in cash at maturity. The notes had no impact on diluted net income per share in any of the prior periods presented.

Income Taxes

Income Taxes	12 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The components of the Company's income tax expense are as follows: Year Ended September 30, Nine Months Ended 2020 2019 (In millions) Current tax expense (benefit): Federal $ (7.6) $ (0.3) $ (0.5) State and other 0.9 0.3 — (6.7) — (0.5) Deferred tax expense (benefit): Federal 21.2 9.1 (23.5) State and other 1.9 0.3 (1.3) 23.1 9.4 (24.8) Income tax expense (benefit) $ 16.4 $ 9.4 $ (25.3) A reconciliation of the federal statutory rate to the Company's effective income tax rate follows: Year Ended September 30, Nine Months Ended 2020 2019 Federal statutory rate 21 % 21 % 21 % State, net of federal benefit 3 1 4 Valuation allowance — — (81) Tax benefits previously unrecognized (2) — — Tax rate benefit in carryback years (1) — — Noncontrolling interests — (1) (1) Effective tax rate (benefit) 21 % 21 % (57) % The effective tax rate for fiscal 2020 includes a tax benefit of $2.3 million related to the net operating loss (NOL) carryback provisions of the Coronavirus Aid, Relief, and Economic Security Act (CARES Act), which allows the Company to carryback a portion of its fiscal 2018 NOL. The carryback provisions result in the recognition of previously unrecognized tax benefits and the revaluation of deferred tax assets due to the utilization of NOLs at a higher tax rate in the carryback period. The Company's effective tax rate for the nine months ended September 30, 2018 also includes a benefit for the release of its federal valuation allowance and a portion of its state valuation allowance associated with its deferred tax assets. The effective tax rate for all periods includes an expense for state income taxes and nondeductible expenses and a benefit related to noncontrolling interests. Significant components of deferred taxes are: September 30, 2020 2019 (In millions) Deferred tax assets: Real estate $ 10.5 $ 10.2 Employee benefits 1.5 1.5 Net operating loss carryforwards 1.7 15.1 AMT credits — 0.6 Accruals not deductible until paid 0.2 0.2 Total deferred tax assets 13.9 27.6 Valuation allowance (1.5) (3.3) Total deferred tax assets, net of valuation allowance 12.4 24.3 Deferred tax liabilities: Deferral of profit on lot sales (18.1) (6.4) Convertible debt — (0.5) Total deferred tax liabilities (18.1) (6.9) Deferred tax (liability) asset, net $ (5.7) $ 17.4 In October 2017, D.R. Horton acquired 75% of the Company's common stock resulting in an ownership change under Section 382 of the Internal Revenue Code. Section 382 limits the Company's ability to use certain tax attributes and built-in losses and deductions in a given year. Any federal tax attributes or built-in losses and deductions that were limited in fiscal 2018 or 2019 have been fully utilized. At September 30, 2020, the Company had no federal NOL carryforwards as a result of NOL carryback claims and taxable income in the current year. At September 30, 2020, the Company had tax benefits of $1.7 million related to state NOL carryforwards, of which $1.4 million will expire between 2030 and 2037 while the remaining $0.3 million do not have an expiration date. The Company has a valuation allowance of $1.5 million and $3.3 million at September 30, 2020 and 2019 because it is more likely than not that a portion of the Company's state deferred tax assets, primarily NOL carryforwards, will not be realized because the Company is no longer operating in some states or the NOL carryforward periods are too brief to realize the related deferred tax asset. The current year decrease in the valuation allowance is primarily attributable to the write-off of state deferred tax assets for NOLs which are not expected to be utilized, resulting in no impact to state tax expense. The Company will continue to evaluate both the positive and negative evidence in determining the need for a valuation allowance on its deferred tax assets. Any reversal of the valuation allowance in future periods will impact the effective tax rate. The Company is subject to a Tax Sharing Agreement with D.R. Horton. The agreement sets forth an equitable method for reimbursements of tax liabilities or benefits between the Company and D.R. Horton related to state and local income, margin or franchise tax returns that are filed on a unitary basis with D.R. Horton. In accordance with the agreement, the Company reimbursed D.R. Horton $0.2 million in fiscal 2020 for its tax expense generated in fiscal 2019, and D.R. Horton reimbursed the Company $0.4 million in fiscal 2019 for its tax benefit generated in the nine months ended September 30, 2018. The Company files income tax returns in the U.S. and in various state jurisdictions. The federal statute of limitations for tax years prior to 2016 is closed and the statute of limitations in major state jurisdictions for tax years prior to 2016 is closed. The Company is not currently being audited by the IRS or any state jurisdictions. A reconciliation of the beginning and ending amount of tax benefits not recognized for book purposes is as follows: Year Ended September 30, Nine Months Ended 2020 2019 (In millions) Balance at beginning of period $ 1.6 $ 1.6 $ 1.1 (Decrease) increase for tax positions taken in prior periods (1.6) — 0.5 Balance at end of period $ — $ 1.6 $ 1.6 The Company had no unrecognized tax benefits at September 30, 2020 as a result of the recognition of $1.6 million of previously unrecognized tax benefits during fiscal 2020. All of the $1.6 million of recognized tax benefits affected the Company’s effective tax rate and was attributable to the NOL carryback provisions of the CARES Act allowing previously uncertain tax attributes to be recognized. The Company recognizes interest accrued related to unrecognized tax benefits in income tax expense. In fiscal years 2020, 2019 and in the nine months ended September 30, 2018, no significant interest related to unrecognized tax benefits was recognized. At September 30, 2020, there were no accrued interest or penalties.

Stockholders' Equity (Notes)

Stockholders' Equity (Notes)	12 Months Ended
	Sep. 30, 2020
Stockholders' Equity Attributable to Parent [Abstract]
Stockholders' Equity Note Disclosure [Text Block]	Stockholders' Equity The Company has an effective shelf registration statement filed with the Securities and Exchange Commission (SEC) in September 2018 registering $500 million of equity securities. As of September 30, 2020, $394.3 million remained available for issuance under the shelf registration statement, $100 million of which is reserved for sales under the at-the-market equity offering program discussed below. In August 2020, the Company entered into an equity distribution agreement to issue and sell, from time to time, up to $100 million in aggregate offering price of its common stock through an at-the-market equity offering program. As of September 30, 2020, no shares had been issued under the at-the-market equity offering program.

Compensation Related Costs, Pos

Compensation Related Costs, Postemployment Benefits	12 Months Ended
	Sep. 30, 2020
Employee Benefit Plans [Abstract]
Share-based Payment Arrangement	Employee Benefit Plans Retirement Plans The Company has a 401(k) plan for all employees who have been with the Company for a period of six months or more. The Company matches portions of employees’ voluntary contributions. Additional employer contributions in the form of profit sharing may also be made at the Company’s discretion. The Company recorded expense of $0.4 million, $0.2 million and $0.1 million for matching contributions in fiscal 2020, 2019 and the nine months ended September 30, 2018, respectively. Restricted Stock Units (RSUs) The Company’s Stock Incentive Plan provides for the granting of stock options and restricted stock units to executive officers, other key employees and non-management directors. Restricted stock unit awards may be based on performance (performance-based) or on service over a requisite time period (time-based). RSU equity awards represent the contingent right to receive one share of the Company’s common stock per RSU if the vesting conditions and/or performance criteria are satisfied and have no voting rights during the vesting period. During fiscal 2020, 2019 and in the nine months ended September 30, 2018, the Company granted time-based RSUs that vest annually in equal installments over periods of three Year Ended September 30, Nine Months Ended 2020 2019 Number of Restricted Stock Units Weighted Average Grant Date Fair Value Number of Restricted Stock Units Weighted Average Grant Date Fair Value Number of Restricted Stock Units Weighted Average Grant Date Fair Value Outstanding at beginning of period 200,960 $ 19.68 86,500 $ 18.09 85,994 $ 17.54 Granted 181,325 16.11 149,400 20.24 12,000 22.35 Vested (79,432) 19.58 (23,740) 18.03 (500) 18.40 Cancelled (16,990) 19.10 (11,200) 18.39 (10,994) 18.40 Outstanding at end of period 285,863 $ 17.47 200,960 $ 19.68 86,500 $ 18.09 The total fair value of shares vested on the vesting date during fiscal 2020 and 2019 was $1.6 million and $0.4 million, respectively. Total stock-based compensation expense related to the Company's restricted stock units for fiscal 2020, 2019 and the nine months ended September 30, 2018 was $2.0 million, $1.3 million and $0.3 million, respectively, and fiscal 2020 and 2019 included $0.5 million and $0.6 million, respectively, of expense recognized for employees that were retirement eligible on the date of grant. These expenses are included in selling, general and administrative expense in the Company's consolidated statements of operations. At September 30, 2020, there was $3.2 million of unrecognized compensation expense related to unvested time-based RSU awards. This expense is expected to be recognized over a weighted average period of 2.6 years.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Other Contingencies	Commitments and Contingencies Contractual Obligations and Off-Balance Sheet Arrangements In support of the Company's residential lot development business, it issues letters of credit under the revolving credit facility and has a surety bond program that provides financial assurance to beneficiaries related to the execution and performance of certain development obligations. At September 30, 2020, the Company had outstanding letters of credit of $36.0 million under the revolving credit facility and surety bonds of $236.9 million issued by third parties to secure performance under various contracts. The Company expects that its performance obligations secured by these letters of credit and bonds will generally be completed in the ordinary course of business and in accordance with the applicable contractual terms. When the Company completes its performance obligations, the related letters of credit and bonds are generally released shortly thereafter, leaving the Company with no continuing obligations. The Company has no material third-party guarantees. Litigation The Company is involved in various legal proceedings that arise from time to time in the ordinary course of business and believes that adequate reserves have been established for any probable losses. The Company does not believe that the outcome of any of these proceedings will have a significant adverse effect on its financial position, long-term results of operations or cash flows. It is possible, however, that charges related to these matters could be significant to the Company's results or cash flows in any one accounting period. Other Commitments The Company leases facilities and equipment under non-cancelable long-term operating lease agreements. In addition, the Company has various obligations under other office space and equipment leases of less than one year. Rent expense for facilities and equipment was $1.1 million in fiscal 2020, $0.7 million in fiscal 2019 and $0.6 million in the nine months ended September 30, 2018. Future minimum rental commitments, by fiscal year, under non-cancelable operating leases having an initial or remaining term in excess of one year are: 2021 — $1.2 million; 2022 — $0.9 million; 2023 — $0.9 million; 2024 — $0.7 million; 2025 — $0.3 million; and thereafter — $0.0 million.

Related Party Disclosures

Related Party Disclosures	12 Months Ended
	Sep. 30, 2020
Related Party Transactions [Abstract]
Related Party Transactions Disclosure [Text Block]	Related Party Transactions The Company has a Shared Services Agreement with D.R. Horton whereby D.R. Horton provides the Company with certain administrative, compliance, operational and procurement services. During fiscal 2020, 2019 and the nine months ended September 30, 2018, the Company paid D.R. Horton $5.0 million, $2.1 million and $0.9 million for these shared services and $2.7 million, $1.4 million and $0.9 million for the cost of health insurance and other employee benefits. These expenses are included in selling, general and administrative expense in the consolidated statements of operations. The Company is subject to a Tax Sharing Agreement with D.R. Horton. The agreement sets forth an equitable method for reimbursements of tax liabilities or benefits between the Company and D.R. Horton related to state and local income, margin or franchise tax returns that are filed on a unitary basis with D.R. Horton. In accordance with the agreement, the Company reimbursed D.R. Horton $0.2 million in fiscal 2020 for its tax expense generated in fiscal 2019, and D.R. Horton reimbursed the Company $0.4 million in fiscal 2019 for its tax benefit generated in the nine months ended September 30, 2018. Under the terms of the Master Supply Agreement with D.R. Horton, both companies identify land development opportunities to expand Forestar's portfolio of assets. At September 30, 2020 and 2019, the Company owned or controlled through purchase contracts approximately 60,500 and 38,300 residential lots, of which D.R. Horton had the following involvement. September 30, 2020 2019 (Dollars in millions) Residential lots under contract to sell to D.R. Horton 14,000 12,800 Residential lots subject to right of first offer with D.R. Horton 16,400 10,600 Earnest money deposits from D.R. Horton for lots under contract $ 92.2 $ 88.7 Earnest money notes from D.R. Horton for lots under contract $ 4.8 $ — Remaining purchase price of lots under contract with D.R. Horton $ 1,022.2 $ 953.8 During fiscal 2020, 2019 and the nine months ended September 30, 2018, the Company's residential lot sales totaled 10,373, 4,132 and 1,024, and lot sales revenues were $880.3 million, $351.7 million and $72.0 million. Lot and land sales to D.R. Horton during those periods were as follows. Year Ended September 30, Nine Months Ended 2020 2019 (Dollars in millions) Residential single-family lots sold to D.R. Horton 10,164 3,728 642 Residential lot sales revenues from sales to D.R. Horton $ 859.7 $ 311.7 $ 43.6 Residential tract acres sold to D.R. Horton 143 290 79 Residential tract sales revenues from sales to D.R. Horton $ 25.6 $ 10.9 $ 2.0 In addition, the net impact of the change in contract liabilities or revenue deferrals increased revenues on lot sales to D.R. Horton by $2.3 million and $4.0 million in fiscal 2020 and 2019, respectively, and decreased revenues by $6.4 million in the nine months ended September 30, 2018. During the nine months ended September 30, 2018, a venture in which the Company owns a 37.5% interest sold 40 residential tract acres to D.R. Horton for $7.8 million. The Company's share of these earnings was $2.5 million, which is included in equity in earnings of unconsolidated ventures in its consolidated statements of operations. During fiscal 2020, 2019 and the nine months ended September 30, 2018, the Company reimbursed D.R. Horton approximately $27.0 million, $34.5 million and $21.2 million for previously paid earnest money and $36.3 million, $13.1 million and $15.2 million for pre-acquisition and other due diligence and development costs related to land purchase contracts whereby D.R. Horton assigned its rights under these land purchase contracts to the Company. During fiscal 2020, 2019 and the nine months ended September 30, 2018, the Company paid D.R. Horton $6.2 million, $2.4 million and $0.6 million for land development services. These amounts are included in cost of sales in the Company’s consolidated statements of operations. At September 30, 2020 and 2019, undeveloped land was $5.4 million and $17.1 million. Undeveloped land primarily consists of undeveloped land which the Company has the contractual right to sell to D.R. Horton within approximately one year of its purchase or, if D.R. Horton elects, at an earlier date, at a sales price equal to the carrying value of the land at the time of sale plus additional consideration of 16% per annum. In fiscal 2019, the Company sold approximately 63 acres of undeveloped land to a third party for approximately $44.2 million. In conjunction with the sale, the Company paid D.R. Horton a fee of approximately $2.1 million to terminate an existing purchase and sale agreement whereby D.R. Horton had the option to purchase the property at a fixed price. This termination fee is included in cost of sales in the Company's consolidated statements of operations. At September 30, 2020 and 2019, accrued expenses and other liabilities on the Company's consolidated balance sheets included $8.4 million and $2.2 million owed to D.R. Horton for any accrued and unpaid shared service charges, land purchase contract deposits and due diligence and other development cost reimbursements.

Summary of Quarterly Results of

Summary of Quarterly Results of Operations (Unaudited)	12 Months Ended
	Sep. 30, 2020
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Results of Operations (Unaudited)	Quarterly Results of Operations (Unaudited) Consolidated quarterly results of operations for fiscal year 2020 and 2019 were (in millions, except per share amounts): 2020 Three Months Three Months Three Months Three Months Total revenues $ 247.2 $ 159.1 $ 177.9 $ 347.6 Income before income taxes 22.2 13.7 10.3 32.0 Income tax expense 5.4 3.3 0.2 7.5 Net income 16.8 10.4 10.1 24.5 Net (loss) income attributable to noncontrolling interests (0.1) 0.8 — 0.3 Net income attributable to Forestar Group Inc. 16.9 9.6 10.1 24.2 Net income per share — basic $ 0.35 $ 0.20 $ 0.21 $ 0.50 Net income per share — diluted $ 0.35 $ 0.20 $ 0.21 $ 0.50 2019 Three Months Three Months Three Months Three Months Total revenues $ 38.5 $ 65.3 $ 88.2 $ 236.3 Income before income taxes 4.9 16.4 8.4 16.0 Income tax expense 1.0 3.6 1.5 3.4 Net income 3.9 12.8 6.9 12.6 Net income (loss) attributable to noncontrolling interests 0.6 2.7 — (0.1) Net income attributable to Forestar Group Inc. 3.3 10.1 6.9 12.7 Net income per share — basic $ 0.08 $ 0.24 $ 0.16 $ 0.30 Net income per share — diluted $ 0.08 $ 0.24 $ 0.16 $ 0.30

Accounting Policies (Policies)

Accounting Policies (Policies)	12 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Basis of Accounting, Policy	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with U.S. Generally Accepted Accounting Principles (GAAP) and include the accounts of Forestar Group Inc. (Forestar) and all of its 100% owned, majority-owned and controlled subsidiaries, which are collectively referred to as the Company unless the context otherwise requires. The Company accounts for its investment in other entities in which it has significant influence over operations and financial policies using the equity method. All intercompany accounts, transactions and balances have been eliminated in consolidation. Noncontrolling interests in consolidated pass-through entities are recognized before income taxes. The transactions included in net income in the consolidated statements of operations are the same as those that would be presented in comprehensive income. Thus, the Company's net income equates to comprehensive income. In October 2017, Forestar became a majority-owned subsidiary of D.R. Horton, Inc. (D.R. Horton) by virtue of a merger with a wholly-owned subsidiary of D.R. Horton. Immediately following the merger, D.R. Horton owned 75% of the Company's outstanding common stock. In connection with the merger, the Company entered into certain agreements with D.R. Horton including a Stockholder’s Agreement, a Master Supply Agreement and a Shared Services Agreement. D.R. Horton is considered a related party of Forestar under GAAP. At September 30, 2020, D.R. Horton owned approximately 65% of the Company's outstanding common stock.
Fiscal Period, Policy	Change in Fiscal Year Following the merger with D.R. Horton, the Company changed its fiscal year-end from December 31 to September 30, effective January 1, 2018. This change aligned Forestar's fiscal year-end reporting calendar with D.R. Horton. The Company's results of operations, cash flows and all transactions impacting stockholders' equity presented in this Form 10-K are for the fiscal years ended September 30, 2020 and 2019 and for the nine months ended September 30, 2018 unless otherwise noted. This Form 10-K also includes an unaudited statement of operations for the comparable stub period of January 1, 2017 to September 30, 2017. See Note 17.
Use of Estimates, Policy	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions. These estimates and assumptions affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ materially from those estimates.
New Accounting Pronouncements, Policy	Adoption of New Accounting Standard In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-02, “Leases,” which requires that lease assets and liabilities be recognized on the balance sheet and that key information about leasing arrangements be disclosed. The guidance was effective for the Company beginning October 1, 2019 and did not have a material impact on its consolidated financial position, results of operations or cash flows. As a result of the adoption of this standard on October 1, 2019, the Company recorded right of use assets of $2.7 million and lease liabilities of $2.9 million. Lease right of use assets are included in other assets and lease liabilities are included in accrued expenses and other liabilities in the consolidated balance sheet.
Revenue	Revenue Recognition Real estate revenue and related profit are generally recognized at the time of the closing of a sale, when title to and possession of the property are transferred to the buyer. The Company’s performance obligation, to deliver the agreed-upon land or lots, is generally satisfied at closing. However, there may be instances in which the Company has an unsatisfied remaining performance obligation at the time of closing. In these instances, the Company records contract liabilities and recognizes those revenues over time as the performance obligations are completed. Generally, the Company's unsatisfied remaining performance obligations are expected to have an original duration of less than one year. See Note 4.
Cash and Cash Equivalents, Policy	Cash and Cash Equivalents Cash and cash equivalents include cash, other short-term instruments with original maturities of three months or less and proceeds from land and lot closings held for the Company’s benefit at title companies.
Real Estate, Policy	Real Estate and Cost of Sales Real estate includes the costs of direct land and lot acquisition, land development, capitalized interest, and direct overhead costs incurred during land development. All indirect overhead costs, such as compensation of management personnel and insurance costs, are charged to selling, general and administrative expense as incurred. Land and development costs are typically allocated to individual residential lots based on the relative sales value of the lot. Cost of sales includes applicable land and lot acquisition, land development and related costs (both incurred and estimated to be incurred) allocated to each residential lot in the project. Any changes to the estimated total development costs subsequent to the initial lot sales are generally allocated to the remaining lots. The Company receives earnest money deposits from homebuilders for purchases of developed lots. These earnest money deposits are typically released to the homebuilders as lots are sold. Earnest money deposits from D.R. Horton are subject to mortgages which are secured by the real estate under contract with D.R. Horton. These mortgages expire when the earnest money is released to D.R. Horton as lots are sold. See Note 15 for related party transactions and balances. The Company has agreements with certain utility or improvement districts to convey water, sewer and other infrastructure-related assets it has constructed in connection with projects within their jurisdiction and receive reimbursements for the cost of these improvements. The reimbursement amounts for these improvements are defined by the district and are based on the allowable costs of the improvements. The transfer is consummated and the Company generally receives payment when the districts have a sufficient tax base to support funding of their bonds. The cost incurred by the Company in constructing these improvements, net of the amount expected to be collected in the future, is included in the Company's land development budgets and in the determination of lot costs. The Company reviews real estate assets held for use for impairment when events or circumstances indicate that their carrying value may not be recoverable. Impairment exists if the carrying amount of the asset is not recoverable from the undiscounted cash flows expected from its use and eventual disposition. The amount of the impairment loss is determined by comparing the carrying value of the asset to its estimated fair value, which is generally determined based on the present value of future cash flows expected from the sale of the asset. Real estate impairments are included in cost of sales in the consolidated statements of operations. See Note 3.
Inventory, Interest Capitalization Policy	Capitalized Interest The Company capitalizes interest costs throughout the development period (active real estate). Capitalized interest is charged to cost of sales as the related real estate is sold to the buyer. During periods in which the Company’s active real estate is lower than its debt level, a portion of the interest incurred is reflected as interest expense in the period incurred. During fiscal 2020 and 2019, the Company’s active real estate exceeded its debt level, and all interest incurred was capitalized to real estate. See Note 5.
Property, Plant and Equipment, Policy	Property and Equipment Property and equipment are stated at cost less accumulated depreciation. The cost of significant additions and improvements is capitalized and the cost of repairs and maintenance is expensed as incurred. Depreciation generally is recorded using the straight-line method over the estimated useful life of the asset as follows: Estimated Useful Lives September 30, 2020 2019 (In millions) Leasehold improvements 5 to 10 years $ 1.2 $ 0.9 Property and equipment 2 to 10 years 1.1 3.4 Total property and equipment 2.3 4.3 Accumulated depreciation (1.2) (1.9) Property and equipment, net $ 1.1 $ 2.4 Depreciation expense was $0.3 million, $0.3 million and $0.2 million in fiscal 2020, 2019 and the nine months ended September 30, 2018, respectively.
Income Tax, Policy	Income Taxes The Company’s income tax expense is calculated using the asset and liability method, under which deferred tax assets and liabilities are recognized based on the future tax consequences attributable to temporary differences between the financial statement amounts of assets and liabilities and their respective tax bases and attributable to net operating losses and tax credit carryforwards. When assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some portion or all of its deferred tax assets will not be realized. The realization of deferred tax assets is dependent upon the generation of sufficient taxable income in future periods and in the jurisdictions in which those temporary differences become deductible. The Company records a valuation allowance when it determines it is more likely than not that a portion of the deferred tax assets will not be realized. The accounting for deferred taxes is based upon estimates of future results. Differences between the anticipated and actual outcomes of these future results could have a material impact on the Company’s consolidated results of operations or financial position. Also, changes in existing federal and state tax laws and tax rates could affect future tax results and the valuation of the Company’s deferred tax assets and liabilities. Interest and penalties related to unrecognized tax benefits are recognized in the financial statements as a component of income tax expense. Significant judgment is required to evaluate uncertain tax positions. The Company evaluates its uncertain tax positions on a quarterly basis. The evaluations are based upon a number of factors, including changes in facts or circumstances, changes in tax law, correspondence with tax authorities during the course of audits and effective settlement of audit issues. Changes in the recognition or measurement of uncertain tax positions could result in increases or decreases in the Company’s income tax expense in the period in which the change is made. See Note 11.
Share-based Payment Arrangement	Stock-Based Compensation The Company’s stockholders formally authorize shares of its common stock to be available for future grants of stock-based compensation awards. From time to time, the Compensation Committee of the Company’s Board of Directors authorizes the grant of stock-based compensation to its employees and directors from these available shares. At September 30, 2020, the outstanding stock-based compensation awards consist of restricted stock units. Grants of restricted stock units vest over a certain number of years as determined by the Compensation Committee of the Board of Directors. Restricted stock units outstanding at September 30, 2020 have a remaining vesting period of 1 to 5 years. The compensation expense for stock-based awards is based on the fair value of the award and is recognized on a straight-line basis over the remaining vesting period. The fair values of restricted stock units are based on the Company’s stock price at the date of grant. See Note 13.
Fair Value Measurement, Policy	Fair Value Measurements The FASB's authoritative guidance for fair value measurements establishes a three-level hierarchy based upon the inputs to the valuation model of an asset or liability. When available, the Company uses quoted market prices in active markets to determine fair value. Non-financial assets measured at fair value on a non-recurring basis principally include real estate assets which the Company reviews for indicators of impairment when events and circumstances indicate that the carrying value is not recoverable. See Note 9.
Description of New Accounting Pronouncements Not yet Adopted	Pending Accounting Standards In June 2016, the FASB issued ASU 2016-13, “Financial Instruments - Credit Losses,” which replaces the current incurred loss impairment methodology with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information in determining credit loss estimates. The guidance is effective for the Company beginning October 1, 2020 and is not expected to have a material impact on its consolidated financial position, results of operations or cash flows. In December 2019, the FASB issued ASU 2019-12 related to simplifying the accounting for income taxes. The guidance is effective for the Company beginning October 1, 2021, although early adoption is permitted. The Company is currently evaluating the impact of this guidance, and it is not expected to have a material impact on its consolidated financial position, results of operations or cash flows. In March 2020, the FASB issued ASU 2020-04, “Reference Rate Reform,” which provides optional expedients and exceptions for applying U.S. GAAP to contracts, hedging relationships, and other transactions affected by the discontinuation of the London Interbank Offered Rate (LIBOR) or by another reference rate expected to be discontinued. The guidance was effective beginning March 12, 2020 and can be applied prospectively through December 31, 2022. The Company will adopt this standard when LIBOR is discontinued and does not expect it to have a material impact on its consolidated financial statements and related disclosures.

Accounting Policies (Tables)

Accounting Policies (Tables)	12 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Property, Plant and Equipment	as follows: Estimated Useful Lives September 30, 2020 2019 (In millions) Leasehold improvements 5 to 10 years $ 1.2 $ 0.9 Property and equipment 2 to 10 years 1.1 3.4 Total property and equipment 2.3 4.3 Accumulated depreciation (1.2) (1.9) Property and equipment, net $ 1.1 $ 2.4 Depreciation expense was $0.3 million, $0.3 million and $0.2 million in fiscal 2020, 2019 and the nine months ended September 30, 2018, respectively.

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Segment Revenues and Earnings	Segment results for the nine months ended September 30, 2018 were as follows: Nine Months Ended September 30, 2018 Real Estate Other Items Not Allocated Consolidated (In millions) Revenues $ 78.3 $ — $ — $ 78.3 Cost of sales 48.9 0.6 — 49.5 Selling, general and administrative expense 7.1 0.3 12.0 19.4 Equity in earnings of unconsolidated ventures (4.8) — — (4.8) Gain on sale of assets (1) (18.6) (9.2) — (27.8) Interest expense — — 3.7 3.7 Interest and other income (1.8) — (4.6) (6.4) Income before income taxes 47.5 8.3 (11.1) 44.7 Net income attributable to noncontrolling interests 1.2 — — 1.2 Income before income taxes attributable to Forestar Group Inc. $ 46.3 $ 8.3 $ (11.1) $ 43.5 ______________ (1) Gain on sale of ass ets within the real estate segment consisted primarily of a gain of $14.6 million related to the sale of the Company's interest in a multi-family venture near Denver. Gain on sale of assets within the other segment relates to the sale of non-core water interests in Texas, Louisiana, Georgia and Alabama.

Real Estate (Tables)

Real Estate (Tables)	12 Months Ended
	Sep. 30, 2020
Real Estate [Abstract]
Real Estate	Real estate consists of: September 30, 2020 2019 (In millions) Developed and under development projects $ 1,304.3 $ 1,011.8 Undeveloped land 5.4 17.1 $ 1,309.7 $ 1,028.9

Revenue (Tables)

Revenue (Tables)	12 Months Ended
	Sep. 30, 2020
Revenues [Abstract]
Revenue from External Customers by Products and Services [Table Text Block]	Revenues consist of: Year Ended September 30, Nine Months Ended 2020 2019 (In millions) Residential lot sales $ 880.3 $ 351.7 $ 72.0 Residential tract sales 48.6 55.8 3.6 Commercial tract sales 2.5 18.5 2.0 Other 0.4 2.3 0.7 $ 931.8 $ 428.3 $ 78.3

Capitalized Interest (Tables)

Capitalized Interest (Tables)	12 Months Ended
	Sep. 30, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Inventory, Interest Capitalization Policy [Table Text Block]	The following table summarizes the Company’s interest costs incurred, capitalized and expensed in fiscal 2020, 2019 and the nine months ended September 30, 2018. Year Ended September 30, Nine Months Ended 2020 2019 (In millions) Capitalized interest, beginning of period $ 23.7 $ 3.2 $ 0.5 Interest incurred 43.3 25.3 7.3 Interest expensed: Directly to interest expense — — (3.7) Charged to cost of sales (18.3) (4.8) (0.9) Capitalized interest, end of period $ 48.7 $ 23.7 $ 3.2

Investments, Equity Method an_2

Investments, Equity Method and Joint Ventures (Tables)	12 Months Ended
	Sep. 30, 2020
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investments	Combined summarized balance sheet and income statement information for these unconsolidated ventures follows: September 30, 2020 2019 (In millions) Assets: Cash and cash equivalents $ 1.2 $ 1.6 Real estate 6.1 13.6 Other assets 0.2 0.1 Total assets $ 7.5 $ 15.3 Liabilities and Equity: Accounts payable and other liabilities $ 0.2 $ 0.3 Equity 7.3 15.0 Total liabilities and equity $ 7.5 $ 15.3 Forestar's investment in unconsolidated ventures $ 3.6 $ 7.3 Year Ended September 30, Nine Months Ended 2020 2019 (In millions) Revenues $ 3.5 $ 1.9 $ 22.2 Earnings 3.8 1.3 15.1 Forestar's equity in earnings of unconsolidated ventures 0.7 0.5 4.8

Other Assets, Accrued Expense_2

Other Assets, Accrued Expenses and Other Liabilities (Tables)	12 Months Ended
	Sep. 30, 2020
Other Assets, Accrued Expenses and Other Liabilities [Abstract]
Schedule of Other Assets and Other Liabilities [Table Text Block]	The Company's other assets at September 30, 2020 and 2019 were as follows: September 30, 2020 2019 (In millions) Receivables, net $ 0.4 $ 1.1 Earnest money notes receivable on sales contracts 4.8 — Lease right of use assets 3.6 — Prepaid expenses 4.9 3.4 Land purchase contract deposits 5.5 5.1 Other assets 5.7 4.1 $ 24.9 $ 13.7 The Company's accrued expenses and other liabilities at September 30, 2020 and 2019 were as follows: September 30, 2020 2019 (In millions) Accrued employee compensation and benefits $ 6.2 $ 5.6 Accrued property taxes 3.8 2.1 Lease liabilities 3.8 — Accrued interest 14.0 13.5 Contract liabilities 0.2 2.5 Deferred income 9.3 9.3 State income taxes payable 0.5 — Accrued development costs 35.3 35.4 Other accrued expenses 10.2 8.4 Other liabilities 10.5 2.8 $ 93.8 $ 79.6

Debt (Tables)

Debt (Tables)	12 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Debt	The Company's notes payable at their carrying amounts consist of the following: September 30, 2020 2019 (In millions) Unsecured: 3.75% convertible senior notes due 2020 $ — $ 116.7 8.0% senior notes due 2024 (1) 345.2 343.8 5.0% senior notes due 2028 (1) 295.9 — Revolving credit facility — — $ 641.1 $ 460.5

Fair Value (Tables)

Fair Value (Tables)	12 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value, by Balance Sheet Grouping [Table Text Block]	Fair Value at September 30, 2020 Carrying Value Level 1 Level 2 Level 3 Total (in millions) Cash and cash equivalents (a) $ 394.3 $ 394.3 $ — $ — $ 394.3 Debt (b) 641.1 — 673.5 — 673.5 Fair Value at September 30, 2019 Carrying Value Level 1 Level 2 Level 3 Total (in millions) Cash and cash equivalents (a) $ 382.8 $ 382.8 $ — $ — $ 382.8 Debt (b) 460.5 — 497.3 — 497.3

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The computations of basic and diluted earnings per share are as follows: Year Ended September 30, Nine Months Ended 2020 2019 (In millions, except share and per share amounts) Numerator: Net income attributable to Forestar Group Inc. $ 60.8 $ 33.0 $ 68.8 Denominator: Weighted average common shares outstanding — basic 48,037,018 41,974,429 41,938,987 Dilutive effect of stock-based compensation 57,093 30,712 30,069 Total weighted average shares outstanding — diluted 48,094,111 42,005,141 41,969,056 Basic net income per common share attributable to Forestar Group Inc. $ 1.26 $ 0.79 $ 1.64 Diluted net income per common share attributable to Forestar Group Inc. $ 1.26 $ 0.79 $ 1.64

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Tax Expense	The components of the Company's income tax expense are as follows: Year Ended September 30, Nine Months Ended 2020 2019 (In millions) Current tax expense (benefit): Federal $ (7.6) $ (0.3) $ (0.5) State and other 0.9 0.3 — (6.7) — (0.5) Deferred tax expense (benefit): Federal 21.2 9.1 (23.5) State and other 1.9 0.3 (1.3) 23.1 9.4 (24.8) Income tax expense (benefit) $ 16.4 $ 9.4 $ (25.3)
Reconciliation of Federal Statutory Rate to Effective Income Tax Rate on Continuing Operations	A reconciliation of the federal statutory rate to the Company's effective income tax rate follows: Year Ended September 30, Nine Months Ended 2020 2019 Federal statutory rate 21 % 21 % 21 % State, net of federal benefit 3 1 4 Valuation allowance — — (81) Tax benefits previously unrecognized (2) — — Tax rate benefit in carryback years (1) — — Noncontrolling interests — (1) (1) Effective tax rate (benefit) 21 % 21 % (57) %
Significant Components of Deferred Taxes	Significant components of deferred taxes are: September 30, 2020 2019 (In millions) Deferred tax assets: Real estate $ 10.5 $ 10.2 Employee benefits 1.5 1.5 Net operating loss carryforwards 1.7 15.1 AMT credits — 0.6 Accruals not deductible until paid 0.2 0.2 Total deferred tax assets 13.9 27.6 Valuation allowance (1.5) (3.3) Total deferred tax assets, net of valuation allowance 12.4 24.3 Deferred tax liabilities: Deferral of profit on lot sales (18.1) (6.4) Convertible debt — (0.5) Total deferred tax liabilities (18.1) (6.9) Deferred tax (liability) asset, net $ (5.7) $ 17.4
Summary of Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of tax benefits not recognized for book purposes is as follows: Year Ended September 30, Nine Months Ended 2020 2019 (In millions) Balance at beginning of period $ 1.6 $ 1.6 $ 1.1 (Decrease) increase for tax positions taken in prior periods (1.6) — 0.5 Balance at end of period $ — $ 1.6 $ 1.6

Compensation Related Costs, P_2

Compensation Related Costs, Postemployment Benefits (Tables)	12 Months Ended
	Sep. 30, 2020
Employee Benefit Plans [Abstract]
Schedule of Nonvested Restricted Stock Units Activity	The following table provides additional information related to time-based RSU activity during those periods. Year Ended September 30, Nine Months Ended 2020 2019 Number of Restricted Stock Units Weighted Average Grant Date Fair Value Number of Restricted Stock Units Weighted Average Grant Date Fair Value Number of Restricted Stock Units Weighted Average Grant Date Fair Value Outstanding at beginning of period 200,960 $ 19.68 86,500 $ 18.09 85,994 $ 17.54 Granted 181,325 16.11 149,400 20.24 12,000 22.35 Vested (79,432) 19.58 (23,740) 18.03 (500) 18.40 Cancelled (16,990) 19.10 (11,200) 18.39 (10,994) 18.40 Outstanding at end of period 285,863 $ 17.47 200,960 $ 19.68 86,500 $ 18.09

Related Party Disclosures (Tabl

Related Party Disclosures (Tables)	12 Months Ended
	Sep. 30, 2020
Related Party Transactions [Abstract]
Schedule of Related Party Transactions [Table Text Block]	September 30, 2020 2019 (Dollars in millions) Residential lots under contract to sell to D.R. Horton 14,000 12,800 Residential lots subject to right of first offer with D.R. Horton 16,400 10,600 Earnest money deposits from D.R. Horton for lots under contract $ 92.2 $ 88.7 Earnest money notes from D.R. Horton for lots under contract $ 4.8 $ — Remaining purchase price of lots under contract with D.R. Horton $ 1,022.2 $ 953.8 During fiscal 2020, 2019 and the nine months ended September 30, 2018, the Company's residential lot sales totaled 10,373, 4,132 and 1,024, and lot sales revenues were $880.3 million, $351.7 million and $72.0 million. Lot and land sales to D.R. Horton during those periods were as follows. Year Ended September 30, Nine Months Ended 2020 2019 (Dollars in millions) Residential single-family lots sold to D.R. Horton 10,164 3,728 642 Residential lot sales revenues from sales to D.R. Horton $ 859.7 $ 311.7 $ 43.6 Residential tract acres sold to D.R. Horton 143 290 79 Residential tract sales revenues from sales to D.R. Horton $ 25.6 $ 10.9 $ 2.0

Summary of Quarterly Results _2

Summary of Quarterly Results of Operations (Unaudited) (Tables)	12 Months Ended
	Sep. 30, 2020
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Results of Operations	Consolidated quarterly results of operations for fiscal year 2020 and 2019 were (in millions, except per share amounts): 2020 Three Months Three Months Three Months Three Months Total revenues $ 247.2 $ 159.1 $ 177.9 $ 347.6 Income before income taxes 22.2 13.7 10.3 32.0 Income tax expense 5.4 3.3 0.2 7.5 Net income 16.8 10.4 10.1 24.5 Net (loss) income attributable to noncontrolling interests (0.1) 0.8 — 0.3 Net income attributable to Forestar Group Inc. 16.9 9.6 10.1 24.2 Net income per share — basic $ 0.35 $ 0.20 $ 0.21 $ 0.50 Net income per share — diluted $ 0.35 $ 0.20 $ 0.21 $ 0.50 2019 Three Months Three Months Three Months Three Months Total revenues $ 38.5 $ 65.3 $ 88.2 $ 236.3 Income before income taxes 4.9 16.4 8.4 16.0 Income tax expense 1.0 3.6 1.5 3.4 Net income 3.9 12.8 6.9 12.6 Net income (loss) attributable to noncontrolling interests 0.6 2.7 — (0.1) Net income attributable to Forestar Group Inc. 3.3 10.1 6.9 12.7 Net income per share — basic $ 0.08 $ 0.24 $ 0.16 $ 0.30 Net income per share — diluted $ 0.08 $ 0.24 $ 0.16 $ 0.30

Accounting Policies (Details)

Accounting Policies (Details) $ in Millions	Sep. 30, 2020USD ($)	Feb. 08, 2018USD ($)aLotProject	Oct. 05, 2017	Sep. 30, 2018USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Oct. 01, 2019USD ($)
Accounting Policies [Abstract]
Operating Lease, Right-of-Use Asset	$ 3.6				$ 3.6	$ 0	$ 2.7
Operating Lease, Liability	3.8				3.8	0	$ 2.9
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	2.3				2.3	4.3
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(1.2)				(1.2)	(1.9)
Property and equipment, net	$ 1.1				1.1	2.4
Depreciation				$ 0.2	0.3	0.3
D.R. Horton, Inc. [Member] | Majority Shareholder [Member]
Accounting Policies [Abstract]
Sale of Stock, Percentage of Ownership after Transaction	65.00%		75.00%
Property, Plant and Equipment [Line Items]
Sale of Stock, Percentage of Ownership after Transaction	65.00%		75.00%
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Starwood Land, L.P.. [Member]
Accounting Policies [Abstract]
Number of Projects Sold | Project		24
Disposal Group, Including Discontinued Operation, Consideration		$ 232
Proceeds from Sale of Real Estate		$ 217.5
Property, Plant and Equipment [Line Items]
Number of Projects Sold | Project		24
Disposal Group, Including Discontinued Operation, Consideration		$ 232
Proceeds from Sale of Real Estate		$ 217.5
Multifamily [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Starwood Land, L.P.. [Member]
Accounting Policies [Abstract]
Number of Projects Sold | Project		1
Property, Plant and Equipment [Line Items]
Number of Projects Sold | Project		1
Residential Real Estate [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Starwood Land, L.P.. [Member]
Accounting Policies [Abstract]
Number of Lots | Lot		750
Property, Plant and Equipment [Line Items]
Number of Lots | Lot		750
Land and Land Improvements [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Starwood Land, L.P.. [Member]
Accounting Policies [Abstract]
Number of Lots | Lot		4,000
Property, Plant and Equipment [Line Items]
Number of Lots | Lot		4,000
Land [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Starwood Land, L.P.. [Member]
Accounting Policies [Abstract]
Area of Land | a		730
Property, Plant and Equipment [Line Items]
Area of Land | a		730
Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 1.2				1.2	0.9
Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 1.1				$ 1.1	$ 3.4
Maximum | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life					10 years
Maximum | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life					10 years
Minimum | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life					5 years
Minimum | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life					2 years

Segment Information - Segment R

Segment Information - Segment Revenues and Earnings (Detail) - USD ($) $ in Millions	3 Months Ended								9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenues	$ 347.6	$ 177.9	$ 159.1	$ 247.2	$ 236.3	$ 88.2	$ 65.3	$ 38.5	$ 78.3	$ 83.5	$ 931.8	$ 428.3
Cost of sales									49.5	90.1	813.7	362.7
Selling, general and administrative expense									19.4	51.2	45.7	28.9
Equity in earnings of unconsolidated ventures									(4.8)	(10.9)	(0.7)	(0.5)
Gain on sale of assets									(27.8)	(113.4)	(0.1)	(3)
Interest expense									3.7	6.4	0	0
Interest and other income									(6.4)	(2.4)	(4.9)	(5.5)
Income before income taxes	32	10.3	13.7	22.2	16	8.4	16.4	4.9	44.7	62.5	78.1	45.7
Net income attributable to noncontrolling interests	$ 0.3	$ 0	$ 0.8	$ (0.1)	$ (0.1)	$ 0	$ 2.7	$ 0.6	1.2	$ 0.1	0.9	3.3
Income before income taxes attributable to Forestar Group Inc.									43.5
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Segment Reporting Information [Line Items]
Revenues									22.2		$ 3.5	$ 1.9
FMF Littleton [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Segment Reporting Information [Line Items]
Gain on sale of assets									(14.6)
Operating Segments [Member] | Real Estate
Segment Reporting Information [Line Items]
Revenues									78.3
Cost of sales									48.9
Selling, general and administrative expense									7.1
Equity in earnings of unconsolidated ventures									(4.8)
Gain on sale of assets									(18.6)
Interest expense									0
Interest and other income									(1.8)
Income before income taxes									47.5
Net income attributable to noncontrolling interests									1.2
Income before income taxes attributable to Forestar Group Inc.									46.3
Operating Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues									0
Cost of sales									0.6
Selling, general and administrative expense									0.3
Equity in earnings of unconsolidated ventures									0
Gain on sale of assets									(9.2)
Interest expense									0
Interest and other income									0
Income before income taxes									8.3
Net income attributable to noncontrolling interests									0
Income before income taxes attributable to Forestar Group Inc.									8.3
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenues									0
Cost of sales									0
Selling, general and administrative expense									12
Equity in earnings of unconsolidated ventures									0
Gain on sale of assets									0
Interest expense									3.7
Interest and other income									(4.6)
Income before income taxes									(11.1)
Net income attributable to noncontrolling interests									0
Income before income taxes attributable to Forestar Group Inc.									$ (11.1)

Real Estate - Real Estate Table

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

Real Estate - Text (Detail)

Real Estate - Text (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2020	Sep. 30, 2019
Real Estate Properties [Line Items]
Payments to Acquire Residential Real Estate		$ 550.8
Payments to Develop Real Estate Assets		503
Inventory Write-down	$ 0.3	0	$ 0.8
Due Diligence Write-Offs		$ 0.9	$ 0.2
D.R. Horton, Inc. [Member]
Real Estate Properties [Line Items]
Related Party Transaction, Rate		16.00%

Revenue (Details)

Revenue (Details) - USD ($) $ in Millions	3 Months Ended								9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2020	Sep. 30, 2019
Revenue from External Customer [Line Items]
Other Revenue (Expense) from Real Estate Operations									$ 0.7		$ 0.4	$ 2.3
Revenues	$ 347.6	$ 177.9	$ 159.1	$ 247.2	$ 236.3	$ 88.2	$ 65.3	$ 38.5	78.3	$ 83.5	931.8	428.3
D.R. Horton, Inc. [Member]
Revenue from External Customer [Line Items]
Revenues									39.1		887.6	326.6
Real Estate | Residential Real Estate [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									72		880.3	351.7
Land [Member] | Residential Real Estate [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									3.6		48.6	55.8
Land [Member] | Commercial Real Estate [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									$ 2		$ 2.5	$ 18.5

Capitalized Interest (Details)

Capitalized Interest (Details) - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2017
Statement [Line Items]
Real Estate Inventory, Capitalized Interest Costs	$ 3.2		$ 48.7	$ 23.7	$ 0.5
Interest Costs Incurred	7.3		43.3	25.3
Interest expense	(3.7)	$ (6.4)	0	0
Real Estate Inventory, Capitalized Interest Costs, Cost of Sales	$ (0.9)		$ (18.3)	$ (4.8)

Investment in Unconsolidated Ve

Investment in Unconsolidated Ventures (Details) $ in Millions	3 Months Ended								9 Months Ended		12 Months Ended
	Sep. 30, 2020USD ($)venture	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2020USD ($)venture	Sep. 30, 2019USD ($)	Dec. 31, 2017USD ($)
Schedule of Equity Method Investments [Line Items]
Cash and cash equivalents	$ 394.3				$ 382.8						$ 394.3	$ 382.8
Real estate	1,309.7				1,028.9						1,309.7	1,028.9
Other assets	24.9				13.7						24.9	13.7
Total assets	1,739.9				1,455.7						1,739.9	1,455.7
Accounts payable and other liabilities	868.1				646.8						868.1	646.8
Equity	871.8				808.9				$ 674.5		871.8	808.9	$ 605.6
Total liabilities and equity	1,739.9				1,455.7						1,739.9	1,455.7
Investment in unconsolidated ventures	3.6				7.3						3.6	7.3
Revenues	347.6	$ 177.9	$ 159.1	$ 247.2	236.3	$ 88.2	$ 65.3	$ 38.5	78.3	$ 83.5	931.8	428.3
Net income	$ 24.5	$ 10.1	$ 10.4	$ 16.8	12.6	$ 6.9	$ 12.8	$ 3.9	70	67.9	61.7	36.3
Income (Loss) from Equity Method Investments									4.8	10.9	0.7	0.5
Return of investment in unconsolidated ventures									0.8		4.3	0.1
Gain on sale of assets									27.8	$ 113.4	$ 0.1	3
Number of Equity Method Investments | venture	4										4
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Schedule of Equity Method Investments [Line Items]
Cash and cash equivalents	$ 1.2				1.6						$ 1.2	1.6
Real estate	6.1				13.6						6.1	13.6
Other assets	0.2				0.1						0.2	0.1
Total assets	7.5				15.3						7.5	15.3
Accounts payable and other liabilities	0.2				0.3						0.2	0.3
Equity	7.3				15						7.3	15
Total liabilities and equity	$ 7.5				$ 15.3						7.5	15.3
Revenues									22.2		3.5	1.9
Net income									15.1		3.8	1.3
Payments to Acquire Equity Method Investments											0
Return of investment in unconsolidated ventures									$ 4.3		$ 4.3	$ 5
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member] | Starwood Land, L.P.. [Member]
Schedule of Equity Method Investments [Line Items]
Number of Equity Method Investments Sold									8
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member] | Lm Land Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Total assets									$ 21.6
Accounts payable and other liabilities									0.4
Equity									21.2
Investment in unconsolidated ventures									8.9
Revenues									17.4
Income (Loss) from Equity Method Investments									6.4
Income (Loss) from Continuing Operations before Income Taxes, Domestic									18.1
Deferred Revenue, Revenue Recognized									5.7
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member] | FOR/SR Forsyth LLC [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from Divestiture of Businesses and Interests in Affiliates									11
Gain on sale of assets									2
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member] | FMF Littleton [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from Divestiture of Businesses and Interests in Affiliates									19.2
Gain on sale of assets									14.6
Real estate and land option charges									$ 3

Other Assets, Accrued Expense_3

Other Assets, Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Oct. 01, 2019	Sep. 30, 2019
Other Assets, Accrued Expenses and Other Liabilities [Abstract]
Accounts and Financing Receivable, after Allowance for Credit Loss	$ 0.4		$ 1.1
Notes Receivable, Related Parties	4.8		0
Operating Lease, Right-of-Use Asset	3.6	$ 2.7	0
Prepaid Expense	4.9		3.4
Deposits Assets	5.5		5.1
Other Assets, Miscellaneous	5.7		4.1
Other assets	24.9		13.7
Employee-related Liabilities	6.2		5.6
Accrual for Taxes Other than Income Taxes	3.8		2.1
Operating Lease, Liability	3.8	$ 2.9	0
Interest Payable	14		13.5
Contract with Customer, Liability, Current	0.2		2.5
Deferred Revenue	9.3		9.3
Taxes Payable	0.5		0
Accrued Development Costs	35.3		35.4
Other Accrued Liabilities	10.2		8.4
Other Liabilities	$ 10.5		$ 2.8
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent		us-gaap:AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent
Accrued expenses and other liabilities	$ 93.8		$ 79.6

Debt - Schedule of Debt (Detail

Debt - Schedule of Debt (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Debt	$ 641.1	$ 460.5
Long-term Line of Credit	0	0
Convertible Debt
Debt Instrument [Line Items]
Debt	$ 0	116.7
Debt Instrument, Interest Rate, Stated Percentage	3.75%
Senior Notes 8%
Debt Instrument [Line Items]
Debt	$ 345.2	343.8
Debt Instrument, Interest Rate, Stated Percentage	8.00%
Senior Notes 5%
Debt Instrument [Line Items]
Debt	$ 295.9	0
Debt Instrument, Interest Rate, Stated Percentage	5.00%
Senior Notes [Member]
Debt Instrument [Line Items]
Debt Issuance Costs, Net	$ 8.9	$ 6.2

Debt - Text (Detail)

Debt - Text (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Apr. 30, 2020	Sep. 30, 2019
Debt Repurchase Program, Authorized Amount		$ 30	$ 30
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity		380
Line of Credit Facility, Maximum Borrowing Capacity		570
Letter of Credit, Maximum Borrowing Capacity		$ 100
Letter of Credit, Maximum Borrowing Capacity, Percentage of Revolving Credit Commitment		50.00%
Repayments of Long-term Lines of Credit		$ 0
Proceeds from Long-term Lines of Credit		0
Long-term Line of Credit		0		$ 0
Letters of Credit Outstanding, Amount		36
Line of Credit Facility, Remaining Borrowing Capacity		$ 344
Convertible Debt
Debt Instrument, Interest Rate, Stated Percentage		3.75%
Maturities of Senior Debt	$ 118.9
Senior Notes 8%
Debt Instrument, Face Amount		$ 350
Debt Instrument, Interest Rate, Stated Percentage		8.00%
Debt Instrument, Redemption Price, Percentage		104.00%
Debt Instrument, Interest Rate, Effective Percentage		8.50%
Senior Notes 5%
Debt Instrument, Face Amount		$ 300
Debt Instrument, Interest Rate, Stated Percentage		5.00%
Debt Instrument, Redemption Price, Percentage		102.50%
Debt Instrument, Interest Rate, Effective Percentage		5.20%

Fair Value, Not Measured at Fai

Fair Value, Not Measured at Fair Value (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	$ 641.1	$ 460.5
Estimate of Fair Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	394.3	382.8
Long-term Debt, Fair Value	673.5	497.3
Cash and cash equivalents	394.3	382.8
Debt	641.1	460.5
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	394.3	382.8
Long-term Debt, Fair Value	0	0
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Long-term Debt, Fair Value	673.5	497.3
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Long-term Debt, Fair Value	$ 0	$ 0

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Forestar Group Inc.	$ 24.2	$ 10.1	$ 9.6	$ 16.9	$ 12.7	$ 6.9	$ 10.1	$ 3.3	$ 68.8	$ 67.8	$ 60.8	$ 33
Weighted average number of common shares									41,938,987	42,200,000	48,037,018	41,974,429
Dilutive effect of stock-based compensation									30,069		57,093	30,712
Adjusted weighted average number of common shares									41,969,056	42,500,000	48,094,111	42,005,141
Basic net income per common share attributable to Forestar Group Inc.	$ 0.50	$ 0.21	$ 0.20	$ 0.35	$ 0.30	$ 0.16	$ 0.24	$ 0.08	$ 1.64	$ 1.61	$ 1.26	$ 0.79
Diluted net income per common share attributable to Forestar Group Inc.	$ 0.50	$ 0.21	$ 0.20	$ 0.35	$ 0.30	$ 0.16	$ 0.24	$ 0.08	$ 1.64	$ 1.59	$ 1.26	$ 0.79
Convertible Debt
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.75%										3.75%
Maturities of Senior Debt			$ 118.9

Income Taxes - Income Tax Expen

Income Taxes - Income Tax Expense Table (Detail) - USD ($) $ in Millions	3 Months Ended								9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2020	Sep. 30, 2019
Current tax provision:
U.S. Federal									$ (0.5)		$ (7.6)	$ (0.3)
State and other									0		0.9	0.3
Total									(0.5)		(6.7)	0
Deferred tax provision:
U.S. Federal									(23.5)		21.2	9.1
State and other									(1.3)		1.9	0.3
Total									(24.8)		23.1	9.4
Income tax expense	$ 7.5	$ 0.2	$ 3.3	$ 5.4	$ 3.4	$ 1.5	$ 3.6	$ 1	$ (25.3)	$ 33.4	$ 16.4	$ 9.4

Income Taxes - Reconciliation T

Income Taxes - Reconciliation Table (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Federal statutory rate	21.00%	21.00%	21.00%
State, net of federal benefit	4.00%	3.00%	1.00%
Valuation allowance	(81.00%)	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Percent	0.00%	(2.00%)	0.00%
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent	0.00%	(1.00%)	0.00%
Noncontrolling interests	(1.00%)	0.00%	(1.00%)
Effective tax rate (benefit)	(57.00%)	21.00%	21.00%

Income Taxes - Deferred Taxes T

Income Taxes - Deferred Taxes Table (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Deferred Tax Assets:
Real estate	$ 10.5	$ 10.2
Employee benefits	1.5	1.5
Net operating loss carryforwards	1.7	15.1
AMT credits	0	0.6
Accruals not deductible until paid	0.2	0.2
Gross deferred tax assets	13.9	27.6
Valuation allowance	(1.5)	(3.3)
Deferred tax asset net of valuation allowance	12.4	24.3
Deferred Tax Liabilities, Tax Deferred Income	(18.1)	(6.4)
Convertible debt	0	(0.5)
Deferred Tax Liabilities:
Total deferred tax liabilities	(18.1)	(6.9)
Deferred Tax Liabilities, Net	$ (5.7)
Deferred tax asset, net		$ 17.4

Income Taxes Income Taxes - Unr

Income Taxes Income Taxes - Unrecognized Tax Benefits Table (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2020	Sep. 30, 2019
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 1,100,000	$ 1,600,000	$ 1,600,000
(Decrease) increase for tax positions taken in prior periods	500,000	(1,600,000)	0
Balance at end of period	1,600,000	0	1,600,000
Unrecognized Tax Benefits, Interest on Income Taxes Expense	0	0	0
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	$ 0	$ 0	$ 0

Income Taxes - Text (Detail)

Income Taxes - Text (Detail) - USD ($)	Sep. 30, 2020	Oct. 05, 2017	Sep. 30, 2018	Sep. 30, 2020	Sep. 30, 2019
Operating Loss Carryforwards [Line Items]
Federal statutory rate			21.00%	21.00%	21.00%
Net operating loss carryforwards	$ 1,700,000			$ 1,700,000	$ 15,100,000
Deferred Tax Assets, Valuation Allowance	(1,500,000)			(1,500,000)	(3,300,000)
Unrecognized Tax Benefits, Interest on Income Taxes Expense			$ 0	0	0
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	0		$ 0	0	0
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount				2,300,000
Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	0			0
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	1,700,000			1,700,000
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	1,400,000			1,400,000
Deferred Tax Assets, Operating Loss Carryforwards, Not Subject to Expiration	$ 300,000			300,000
D.R. Horton, Inc. [Member] | Reimbursement From Parent [Member]
Operating Loss Carryforwards [Line Items]
Related Party Transaction, Amounts of Transaction					$ 400,000
D.R. Horton, Inc. [Member] | Reimbursement To Parent [Member]
Operating Loss Carryforwards [Line Items]
Related Party Transaction, Amounts of Transaction				$ 200,000
Majority Shareholder [Member] | D.R. Horton, Inc. [Member]
Operating Loss Carryforwards [Line Items]
Sale of Stock, Percentage of Ownership after Transaction	65.00%	75.00%

Stockholders' Equity (Details)

Stockholders' Equity (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2018
Class of Stock [Line Items]
Equity Securities Registered, Value		$ 500
Common Stock, Shares Authorized	$ 394.3
At-the-market Equity Offering Program, Common Stock Available for Issuance	$ 100
At-the-market Equity Offering Program, Common Stock Issued	0

Compensation Related Costs, P_3

Compensation Related Costs, Postemployment Benefits (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2017
Defined Contribution Plan, Cost	$ 0.1	$ 0.4	$ 0.2
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value		1.6	$ 0.4
Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount		$ 3.2
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition		2 years 7 months 6 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	86,500	285,863	200,960	85,994
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 18.09	$ 17.47	$ 19.68	$ 17.54
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	12,000	181,325	149,400
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 22.35	$ 16.11	$ 20.24
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	(500)	(79,432)	(23,740)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 18.40	$ 19.58	$ 18.03
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(10,994)	(16,990)	(11,200)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 18.40	$ 19.10	$ 18.39
Restricted Stock Units (RSUs) [Member]
Share-based Payment Arrangement, Expense	$ 0.3	$ 2	$ 1.3
Restricted Stock Units (RSUs) [Member] | Other [Member]
Share-based Payment Arrangement, Expense		$ 0.5	$ 0.6
Minimum | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period		3 years
Maximum | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period		5 years

Commitments and Contingencies (

Commitments and Contingencies (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2020	Sep. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Letters of Credit Outstanding, Amount		$ 36
Special Assessment Bond		236.9
Operating Leases, Rent Expense	$ 0.6	1.1	$ 0.7
Lessee, Operating Lease, Liability, to be Paid, Year One		1.2
Lessee, Operating Lease, Liability, to be Paid, Year Two		0.9
Lessee, Operating Lease, Liability, to be Paid, Year Three		0.9
Lessee, Operating Lease, Liability, to be Paid, Year Four		0.7
Lessee, Operating Lease, Liability, to be Paid, Year Five		0.3
Lessee, Operating Lease, Liability, to be Paid, after Year Five		$ 0

Related Party Disclosures (Deta

Related Party Disclosures (Details) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2018USD ($)aLot	Sep. 30, 2017USD ($)	Sep. 30, 2020USD ($)Lot	Sep. 30, 2019USD ($)aLot
Related Party Transaction [Line Items]
Number of Units in Real Estate Property | Lot			60,500	38,300
Number of Lots Sold | Lot	1,024		10,373	4,132
Income (Loss) from Equity Method Investments	$ 4.8	$ 10.9	$ 0.7	$ 0.5
Real estate			1,309.7	1,028.9
Due to Related Parties, Current			8.4	2.2
D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Deferred Revenue, Period Increase (Decrease)	(6.4)		2.3	4
Related Party Transaction, Purchases from Related Party	0.6		6.2	2.4
Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party	0.9		5	2.1
Related Party Transaction, Expenses from Transactions with Related Party	0.9		2.7	1.4
D.R. Horton, Inc. [Member] | Contract Termination [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction				2.1
D.R. Horton, Inc. [Member] | Reimbursement From Parent [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction				0.4
D.R. Horton, Inc. [Member] | Reimbursement To Parent [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction			0.2
D.R. Horton, Inc. [Member] | Deposits [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	21.2		27	34.5
D.R. Horton, Inc. [Member] | Other Expense [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	15.2		36.3	13.1
Residential Real Estate [Member] | Real Estate
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	$ 72		880.3	351.7
Land [Member]
Related Party Transaction [Line Items]
Real estate			$ 5.4	$ 17.1
D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Number of Lots Sold | Lot	642		10,164	3,728
Revenue from Related Parties	$ 43.6		$ 859.7	$ 311.7
Related Party Transaction, Rate			16.00%
D.R. Horton, Inc. [Member] | Equity Method Investments [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage	37.50%
Area of Land | a	40
Proceeds from Sale of Real Estate	$ 7.8
Income (Loss) from Equity Method Investments	$ 2.5
D.R. Horton, Inc. [Member] | Land [Member]
Related Party Transaction [Line Items]
Number of Lots Sold | Lot	79		143	290
Revenue from Related Parties	$ 2		$ 25.6	$ 10.9
D.R. Horton, Inc. [Member] | Under Contract [Member]
Related Party Transaction [Line Items]
Number of Units in Real Estate Property | Lot			14,000	12,800
Related Party Transaction, Purchase Obligation from Parent			$ 1,022.2	$ 953.8
D.R. Horton, Inc. [Member] | Under Contract [Member] | Cash [Member]
Related Party Transaction [Line Items]
Related Party Deposit Liabilities			92.2	88.7
D.R. Horton, Inc. [Member] | Under Contract [Member] | Notes Payable, Other Payables [Member]
Related Party Transaction [Line Items]
Related Party Deposit Liabilities			$ 4.8	$ 0
D.R. Horton, Inc. [Member] | Right of First Offer [Member]
Related Party Transaction [Line Items]
Number of Units in Real Estate Property | Lot			16,400	10,600
Other Customer [Member] | Equity Method Investments [Member]
Related Party Transaction [Line Items]
Area of Land | a				63
Proceeds from Sale of Real Estate				$ 44.2

Summary of Quarterly Results _3

Summary of Quarterly Results of Operations (Unaudited) (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2020	Sep. 30, 2019
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 347.6	$ 177.9	$ 159.1	$ 247.2	$ 236.3	$ 88.2	$ 65.3	$ 38.5	$ 78.3	$ 83.5	$ 931.8	$ 428.3
Income before income taxes	32	10.3	13.7	22.2	16	8.4	16.4	4.9	44.7	62.5	78.1	45.7
Income tax expense	7.5	0.2	3.3	5.4	3.4	1.5	3.6	1	(25.3)	33.4	16.4	9.4
Net income	24.5	10.1	10.4	16.8	12.6	6.9	12.8	3.9	70	67.9	61.7	36.3
Net income attributable to noncontrolling interests	0.3	0	0.8	(0.1)	(0.1)	0	2.7	0.6	1.2	0.1	0.9	3.3
Net income attributable to Forestar Group Inc.	$ 24.2	$ 10.1	$ 9.6	$ 16.9	$ 12.7	$ 6.9	$ 10.1	$ 3.3	$ 68.8	$ 67.8	$ 60.8	$ 33
Net income (loss) per share -- basic
Basic net income per common share attributable to Forestar Group Inc.	$ 0.50	$ 0.21	$ 0.20	$ 0.35	$ 0.30	$ 0.16	$ 0.24	$ 0.08	$ 1.64	$ 1.61	$ 1.26	$ 0.79
Net income (loss) per share -- diluted
Diluted net income per common share attributable to Forestar Group Inc.	$ 0.50	$ 0.21	$ 0.20	$ 0.35	$ 0.30	$ 0.16	$ 0.24	$ 0.08	$ 1.64	$ 1.59	$ 1.26	$ 0.79

Uncategorized Items - for-20200

Label	Element	Value
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	$ 363,000,000