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Related Party Transactions (Details) $ in Millions	3 Months Ended
Related Party Transactions (Details) $ in Millions	Dec. 31, 2021 USD ($) Lot	Dec. 31, 2020 USD ($) Lot	Sep. 30, 2021 USD ($) Lot
Related Party Transaction [Line Items]
Number of Units in Real Estate Property \| Lot	65,700		64,400
Number of Lots Sold \| Lot	4,516	3,567
D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party	$ 1.0	$ 1.1
Related Party Transaction, Expenses from Transactions with Related Party	1.6	1.0
Costs and Expenses, Related Party	0.9	1.1
Deferred Revenue, Period Increase (Decrease)	2.1	0.2
Related Party Transaction, Purchases from Related Party	0.9	$ 1.7
Due to Related Parties, Current	$ 7.7		$ 6.7
D.R. Horton, Inc. [Member] \| Maximum [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Rate	16.00%
D.R. Horton, Inc. [Member] \| Minimum [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Rate	12.00%
D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Number of Lots Sold \| Lot	4,014	3,389
Revenue from Related Parties	$ 328.0	$ 294.0
Under Contract [Member] \| D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Number of Units in Real Estate Property \| Lot	20,000		21,000
Related Party Transaction, Purchase Obligation from Parent	$ 1,491.5		$ 1,582.7
Under Contract [Member] \| D.R. Horton, Inc. [Member] \| Notes Payable, Other Payables
Related Party Transaction [Line Items]
Related Party Deposit Liabilities	0.6		0.7
Under Contract [Member] \| D.R. Horton, Inc. [Member] \| Cash
Related Party Transaction [Line Items]
Related Party Deposit Liabilities	$ 134.8		$ 143.1
Right of First Offer [Member] \| D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Number of Units in Real Estate Property \| Lot	18,300		18,200
Other Expense [Member] \| D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	$ 21.6	20.9
Deposits [Member] \| D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	2.7	16.1
Real Estate [Member] \| Residential Real Estate [Member]
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	$ 404.1	$ 307.0