Investment in Unconsolidated Entities - Narrative (Details) $ in Millions	Dec. 31, 2017 USD ($) State	Sep. 30, 2017 USD ($)
Schedule of Equity Method Investments [Line Items]
Number of equity method investments | State	15
Investment in unconsolidated entities	$ 86.1	$ 0.0
Outstanding debt, unconsolidated entities	85.1
Nonrecourse Debt [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding debt, unconsolidated entities	79.5
Segment Reconciling Items [Member]
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated entities	$ 21.0