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Related Party Transactions (Details) $ in Millions	3 Months Ended		9 Months Ended
Related Party Transactions (Details) $ in Millions	Jun. 30, 2020 USD ($) Lot	Jun. 30, 2019 USD ($) Lot	Jun. 30, 2020 USD ($) Lot	Jun. 30, 2019 USD ($) Lot	Sep. 30, 2019 USD ($) Lot
Related Party Transaction [Line Items]
Number of Units in Real Estate Property \| Lot	50,700		50,700		38,300
Number of Lots Sold \| Lot	2,023	1,158	6,396	2,224
Real estate	$ 1,287.1		$ 1,287.1		$ 1,028.9
D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party			3.8	$ 1.6
Related Party Transaction, Expenses from Transactions with Related Party			1.9	1.1
Due to Related Parties, Current	3.0		3.0		$ 2.2
Deferred Revenue, Period Increase (Decrease)	2.8	$ (2.0)	2.1	(3.6)
Related Party Transaction, Purchases from Related Party	$ 1.0	$ 0.6	$ 3.9	$ 1.4
Related Party Transaction, Rate			16.00%
D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Number of Lots Sold \| Lot	1,991	995	6,287	1,903
Revenue from Related Parties	$ 159.3	$ 75.2	$ 526.0	$ 145.4
Under Contract [Member] \| D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Number of Units in Real Estate Property \| Lot	14,100		14,100		12,800
Related Party Transaction, Purchase Obligation from Parent	$ 1,016.4		$ 1,016.4		$ 953.8
Under Contract [Member] \| D.R. Horton, Inc. [Member] \| Notes Payable, Other Payables
Related Party Transaction [Line Items]
Related Party Deposit Liabilities	6.5		6.5		0.0
Under Contract [Member] \| D.R. Horton, Inc. [Member] \| Cash
Related Party Transaction [Line Items]
Related Party Deposit Liabilities	$ 91.0		$ 91.0		$ 88.7
Right of First Offer [Member] \| D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Number of Units in Real Estate Property \| Lot	15,500		15,500		10,600
Land [Member]
Related Party Transaction [Line Items]
Real estate	$ 15.4		$ 15.4		$ 17.1
Other Expense [Member] \| D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	12.9	4.7	26.2	8.4
Deposits [Member] \| D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	$ 7.0	$ 10.8	$ 23.2	$ 27.6
Land [Member] \| D.R. Horton, Inc. [Member]
Related Party Transaction [Line Items]
Number of Lots Sold \| Lot	30	0	66	0
Revenue from Related Parties	$ 13.4	$ 0.0	$ 20.6	$ 0.0
Real Estate [Member] \| Residential Real Estate [Member]
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	$ 164.4	$ 87.6	$ 537.9	$ 171.6