Inventory - Narrative (Details) $ in Millions	3 Months Ended	9 Months Ended
	Jun. 30, 2016 property Community	Jun. 30, 2017 USD ($) home Community	Jun. 30, 2016 property Community	Sep. 30, 2016 USD ($) home	Jun. 30, 2016 Community
Inventory Disclosure [Abstract]
Number of substantially completed homes unsold | home		132		178
Total value of substantially completed homes | $		$ 39.0		$ 56.1
Threshold number of homes below a minimum threshold of profitability | home		10
Real Estate Properties [Line Items]
Number of communities on watch list	7	3	7		7
Number of communities requiring further analysis	3	0	3
Number of communities impaired	2		3
West Segment
Real Estate Properties [Line Items]
Number of communities on watch list					4
Number of communities requiring further analysis					2
East Segment
Real Estate Properties [Line Items]
Number of communities on watch list | property	2		2
Number of communities requiring further analysis	1		1		1