Revenue (Details) - USD ($) $ in Millions	3 Months Ended								9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2020	Sep. 30, 2019
Revenue from External Customer [Line Items]
Other Revenue (Expense) from Real Estate Operations									$ 0.7		$ 0.4	$ 2.3
Revenues	$ 347.6	$ 177.9	$ 159.1	$ 247.2	$ 236.3	$ 88.2	$ 65.3	$ 38.5	78.3	$ 83.5	931.8	428.3
D.R. Horton, Inc. [Member]
Revenue from External Customer [Line Items]
Revenues									39.1		887.6	326.6
Real Estate | Residential Real Estate [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									72.0		880.3	351.7
Land [Member] | Residential Real Estate [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									3.6		48.6	55.8
Land [Member] | Commercial Real Estate [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Including Assessed Tax									$ 2.0		$ 2.5	$ 18.5