Consolidated Statements of Operations (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Revenues	$ 247.2	$ 38.5
Cost of sales	216.6	30.7
Selling, general and administrative expense	10.5	5.7
Equity in earnings of unconsolidated ventures	(0.5)	(0.6)
Loss (gain) on sale of assets	0.1	(0.9)
Interest and other income	(1.7)	(1.3)
Income before income taxes	22.2	4.9
Income tax expense	5.4	1.0
Net income	16.8	3.9
Net income (loss) attributable to noncontrolling interests	(0.1)	0.6
Net income attributable to Forestar Group Inc.	$ 16.9	$ 3.3
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING
Basic (in shares)	48,011,132	41,952,493
Diluted (in shares)	48,066,418	41,958,699
Earnings Per Share [Abstract]
Earnings Per Share, Basic	$ 0.35	$ 0.08
NET INCOME (LOSS) PER DILUTED SHARE
Earnings Per Share, Diluted	$ 0.35	$ 0.08