Real Estate Joint Ventures - Summarized Financial Information for Unconsolidated Investments (Details) - Other affiliates - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017
Investments in and Advances to Affiliates [Line Items]
Total assets	$ 10.2		$ 10.8
Accounts payable and other liabilities	0.1		0.5
Equity	10.1		$ 10.3
Net loss	$ 0.3	$ 0.2