Related Parties (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Related Party Transactions [Abstract]
Net accounts receivable, related parties	$ 0.7		$ 0.7		$ 2.0
Accounts payable and accrued expenses, related parties	0.3		0.3		$ 0.4
Joint venture fee income	$ 1.3	$ 1.4	$ 4.6	$ 4.4