Revenues (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue from External Customer [Line Items]
Other	$ 0.1	$ 0.6	$ 0.4	$ 1.9
Revenues	177.9	88.2	584.3	192.0
Real Estate [Member] | Residential Real Estate [Member]
Revenue from External Customer [Line Items]
Residential lot sales	164.4	87.6	537.9	171.6
Land [Member] | Residential Real Estate [Member]
Revenue from External Customer [Line Items]
Residential lot sales	13.4	0.0	43.5	0.0
Land [Member] | Commercial Real Estate [Member]
Revenue from External Customer [Line Items]
Residential lot sales	$ 0.0	$ 0.0	$ 2.5	$ 18.5