Net Income (Loss) per Share - Earnings Attributable to Common Shareholders and Weighted Average Common Shares Outstanding (Tables) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Continuing operations
Net income (loss) attributable to Forestar Group Inc.	$ 10.1	$ 6.9	$ 36.5	$ 20.3
Denominator:
Weighted average common shares outstanding — basic	48,050,379	41,959,866	48,028,957	41,957,408
Dilutive effect of share based compensation	24,831	50,355	45,903	20,931
Total weighted average shares outstanding — diluted	48,075,210	42,010,221	48,074,860	41,978,339
Anti-dilutive awards excluded from diluted weighted average shares (in shares)	0	0	0	0
Earnings Per Share, Basic	$ 0.21	$ 0.16	$ 0.76	$ 0.48
Earnings Per Share, Diluted	$ 0.21	$ 0.16	$ 0.76	$ 0.48