Investment in Unconsolidated Entities - Condensed Financial Information of Unconsolidated Entities (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Assets:
Assets	$ 203.7
Liabilities and Equity:
Debt	85.1
Equity	105.5
Liabilities and Equity	203.7
Revenues	8.7
Net earnings of unconsolidated entities (1)	17.4
Equity in earnings of unconsolidated entities	2.3	$ 0.0
Forestar Group [Member]
Liabilities and Equity:
Equity in earnings of unconsolidated entities	7.6
Accounts Payable [Member]
Liabilities and Equity:
Accounts payable and other liabilities	13.1
Cash and Cash Equivalents [Member]
Assets:
Current assets	13.1
Inventories [Member]
Assets:
Current assets	168.9
Other Assets [Member]
Assets:
Current assets	$ 21.7