Investment in Unconsolidated Entities - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)	Sep. 30, 2017 USD ($)
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated entities	$ 32.1	$ 0.0
Outstanding debt, unconsolidated entities	45.8
Nonrecourse Debt [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding debt, unconsolidated entities	41.2
Segment Reconciling Items [Member]
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated entities	$ 14.8
Forestar Group [Member]
Schedule of Equity Method Investments [Line Items]
Number of Equity Method Investments	6
Number of Equity Method Investments Sold	8
Investment in unconsolidated entities	$ 17.3