Investment in Unconsolidated Ventures - Summarized Income Statement Information (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2020	Jun. 30, 2019
Schedule of Equity Method Investments [Line Items]
Revenues	$ 177.9			$ 88.2			$ 584.3	$ 192.0
Net income	10.1	$ 10.4	$ 16.8	6.9	$ 12.8	$ 3.9	37.2	23.6
Equity in earnings of unconsolidated ventures	(0.1)			0.0			0.6	0.5
Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Revenues	0.0			0.1			3.0	1.9
Net income	$ (0.1)			$ (0.1)			$ 1.9	$ 1.3