Income Taxes - Deferred Taxes Table (Detail) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Components of Deferred Tax Assets [Abstract]
Real estate	$ 16.7	$ 11.9
Corporate AMT credit carryforwards	16.5	0.0
Employee benefits	4.4	3.8
Net operating loss carryforwards	0.7	0.9
Accruals not deductible until paid	1.2	0.8
Total deferred tax assets	39.5	17.4
Valuation allowance	(0.6)	(0.8)
Total deferred tax assets, net of valuation allowance	38.9	16.6
Components of Deferred Tax Liabilities [Abstract]
Deferral of profit on lot sales	(125.1)	(84.1)
Total deferred tax liabilities	(125.1)	(84.1)
Deferred tax liability, net	$ (86.2)	$ (67.5)