Inventory Inventory - Quantitative Unobservable Inputs (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2019 USD ($) home	Sep. 30, 2018 USD ($) home	Sep. 30, 2017 USD ($) home
Quantitative unobservable inputs for inventory impairment [Line Items]
Average selling price (in thousands)		$ 356	$ 405
Minimum
Quantitative unobservable inputs for inventory impairment [Line Items]
Average selling price (in thousands)	$ 350
Closings per community per month | home	1	1	1
Maximum
Quantitative unobservable inputs for inventory impairment [Line Items]
Average selling price (in thousands)	$ 615
Closings per community per month | home	4	6	4
Discount Rate
Quantitative unobservable inputs for inventory impairment [Line Items]
Discount rate		0.1511	0.1283
Discount Rate | Minimum
Quantitative unobservable inputs for inventory impairment [Line Items]
Discount rate	0.1470
Discount Rate | Maximum
Quantitative unobservable inputs for inventory impairment [Line Items]
Discount rate	0.1680