Inventory - Narrative (Details) $ in Millions	6 Months Ended
	Mar. 31, 2018 USD ($) home Community	Sep. 30, 2017 USD ($) home	Mar. 31, 2017 Community
Inventory Disclosure [Abstract]
Number of substantially completed homes unsold | home	126	171
Total value of substantially completed homes | $	$ 40.3	$ 52.6
Threshold number of homes below a minimum threshold of profitability | home	10
Real Estate Properties [Line Items]
Number of communities on watch list	2		6
Number of communities requiring further analysis	0		0
West Segment
Real Estate Properties [Line Items]
Number of communities requiring further analysis	1		5
Southeast Segment
Real Estate Properties [Line Items]
Number of communities requiring further analysis	1
East Segment
Real Estate Properties [Line Items]
Number of communities requiring further analysis			1