Inventory - Narrative (Details) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2016 property Community	Mar. 31, 2017 USD ($) home Community	Mar. 31, 2016 property Community	Sep. 30, 2016 USD ($) home	Mar. 31, 2016 Community
Inventory Disclosure [Abstract]
Number of substantially completed homes unsold | home		119		178
Total value of substantially completed homes | $		$ 34.7		$ 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	9	6	9		2
Number of communities requiring further analysis	2	0	2
Number of communities impaired	1		1
West Segment
Real Estate Properties [Line Items]
Number of communities on watch list		5
East Segment
Real Estate Properties [Line Items]
Number of communities on watch list		1