Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Business Information [Line Items]
Cash and cash equivalents	$ 4,516.4	$ 3,873.6
Advertising expense	72.3	64.7	$ 41.7
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 0.0	1.4
Variable Interest Entity, Consolidated, Notes Payable		118.8
Maximum [Member] | Restricted Stock Units (RSUs) [Member]
Business Information [Line Items]
Remaining vesting period	4 years 10 months 24 days
Forestar Group [Member]
Business Information [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent	62.00%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	38.00%
Subsidiaries [Member]
Business Information [Line Items]
Cash and cash equivalents	$ 78.4	70.2
Variable Interest Entity, Not Primary Beneficiary [Member]
Business Information [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	1,900.0	1,600.0
Accounts Receivable [Member]
Business Information [Line Items]
Cash and cash equivalents	$ 304.9	$ 301.8