Consolidated Statements of Operations (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Revenues	$ 88.2	$ 23.6	$ 192.0	$ 77.0
Cost of sales	75.3	10.0	149.6	48.9
Selling, general and administrative expense	7.9	6.5	19.8	36.1
Equity in earnings of unconsolidated ventures	0.0	(1.0)	(0.5)	(9.6)
Gain on sale of assets	(1.5)	(1.3)	(2.4)	(4.1)
Interest expense	0.0	1.6	0.0	5.8
Interest and other income	(1.9)	(2.6)	(4.1)	(4.8)
INCOME FROM CONTINUING OPERATIONS BEFORE TAXES	8.4	10.4	29.6	4.7
Income tax expense	1.5	0.1	6.0	12.6
NET INCOME (LOSS) FROM CONTINUING OPERATIONS	6.9	10.3	23.6	(7.9)
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAXES	0.0	0.0	0.0	7.2
CONSOLIDATED NET INCOME (LOSS)	6.9	10.3	23.6	(0.7)
Less: Net income attributable to noncontrolling interests	0.0	0.9	3.3	2.9
NET INCOME (LOSS) ATTRIBUTABLE TO FORESTAR GROUP INC.	$ 6.9	$ 9.4	$ 20.3	$ (3.6)
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING
Basic (in shares)	41,959,866	41,938,936	41,957,408	41,945,099
Diluted (in shares)	42,010,221	41,966,313	41,978,339	41,945,099
NET INCOME (LOSS) PER BASIC SHARE
Continuing operations, basic (usd per share)	$ 0.16	$ 0.22	$ 0.48	$ (0.26)
Discontinued operations, basic (usd per share)	0.00	0.00	0.00	0.17
NET INCOME (LOSS) PER BASIC SHARE (usd per share)	0.16	0.22	0.48	(0.09)
NET INCOME (LOSS) PER DILUTED SHARE
Continuing operations, diluted (usd per share)	0.16	0.22	0.48	(0.26)
Discontinued operation, diluted (usd per share)	0.00	0.00	0.00	0.17
NET INCOME (LOSS) PER DILUTED SHARE (usd per share)	$ 0.16	$ 0.22	$ 0.48	$ (0.09)