Income Taxes - Deferred Income Taxes (Details) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Deferred tax assets:
Inventory costs	$ 39.8	$ 40.9
Inventory impairments	27.9	31.8
Warranty and construction defect costs	135.1	121.8
Net operating loss carryforwards	31.5	38.1
Tax credit carryforwards	3.5	4.3
Incentive compensation plans	65.1	55.2
Deferred income	0.2	1.3
Other	7.0	5.8
Total deferred tax assets	310.1	299.2
Valuation allowance	(18.7)	(17.7)
Total deferred tax assets, net of valuation allowance	291.4	281.5
Deferred tax liabilities:
Deferral of profit on home sales	95.4	64.9
Deferred Tax Liabilities, Property, Plant and Equipment	14.2	10.7
Other	18.7	11.9
Total deferred tax liabilities	128.3	87.5
Deferred income taxes, net	$ 163.1	$ 194.0