Income Taxes - Textual (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Operating Loss Carryforwards [Line Items]
Effective tax rate	21.80%	20.20%	23.80%
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	2.20%	3.10%
Federal statutory rate	21.00%	21.00%	21.00%
Net operating loss carryforwards	$ 11.7	$ 17.5
Deferred Tax Assets, Valuation Allowance	4.2	$ 7.5
Forestar Consolidated [Member] | State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	1.4
Home Building | State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	10.3
Home Building | State [Member] | NOL Carryforwards to Expire in One to Ten Years [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, subject to expiration	2.9
Home Building | State [Member] | NOL Carryforward to Expire in Eleven to Twenty Years [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, subject to expiration	$ 7.4