Summary of Significant Accounting Policies - Goodwill (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Goodwill [Line Items]
Goodwill impairment			$ 7.2	$ 9.8	$ 0.0
Homebuilding [Member]
Goodwill [Line Items]
Goodwill impairment	$ 7.2	$ 9.8	7.2	9.8	$ 0.0
Goodwill	80.0	87.2	80.0	87.2
Homebuilding [Member] | East [Member]
Goodwill [Line Items]
Goodwill	21.8	21.8	21.8	21.8
Homebuilding [Member] | Midwest [Member]
Goodwill [Line Items]
Goodwill	0.0	0.0	0.0	0.0
Homebuilding [Member] | Southeast [Member]
Goodwill [Line Items]
Goodwill	40.1	47.3	40.1	47.3
Homebuilding [Member] | South Central [Member]
Goodwill [Line Items]
Goodwill	15.9	15.9	15.9	15.9
Homebuilding [Member] | Southwest [Member]
Goodwill [Line Items]
Goodwill	0.0	0.0	0.0	0.0
Homebuilding [Member] | West [Member]
Goodwill [Line Items]
Goodwill	$ 2.2	$ 2.2	$ 2.2	$ 2.2