CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Earnings Per Share, Diluted [Abstract]
Revenues	$ 301.5	$ 421.6	$ 518.2	$ 829.2
Cost of sales	245.6	334.1	414.8	668.3
Selling, General and Administrative Expense	22.0	24.3	44.9	45.8
Equity in earnings of unconsolidated ventures	0.0	0.0	0.0	(1.1)
Gain on sale of assets	0.0	0.0	(1.6)	(0.5)
Interest and other income	(2.0)	0.0	(3.7)	0.0
Income before income taxes	35.9	63.2	63.8	116.7
Income tax expense	9.0	15.4	16.1	28.4
Net income	26.9	47.8	47.7	88.3
Net income attributable to noncontrolling interests	0.0	0.0	0.0	0.0
Net income attributable to Forestar Group Inc.	$ 26.9	$ 47.8	$ 47.7	$ 88.3
Basic net income per common share attributable to Forestar Group Inc.	$ 0.54	$ 0.96	$ 0.95	$ 1.77
Weighted average number of common shares	49,943,373	49,820,937	49,916,927	49,752,153
Diluted net income per common share attributable to Forestar Group Inc.	$ 0.54	$ 0.96	$ 0.95	$ 1.77
Adjusted weighted average number of common shares	50,010,539	49,878,166	49,954,781	49,805,517