Investment in Unconsolidated Entities - Condensed Financial Information of Unconsolidated Entities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Assets:
Assets	$ 94.8		$ 94.8
Liabilities and Equity:
Debt	45.6		45.6
Equity	47.2		47.2
Liabilities and Equity	94.8		94.8
Revenues	2.8		14.9
Net earnings of unconsolidated entities	2.7		24.4
Equity in earnings of unconsolidated entities	0.4	$ 0.0	3.1	$ 0.0
Forestar Group [Member]
Liabilities and Equity:
Equity in earnings of unconsolidated entities	1.0		10.1
Accounts Payable [Member]
Liabilities and Equity:
Accounts payable and other liabilities	2.0		2.0
Cash and Cash Equivalents [Member]
Assets:
Current assets	5.8		5.8
Inventories [Member]
Assets:
Current assets	88.0		88.0
Other Assets [Member]
Assets:
Current assets	$ 1.0		$ 1.0