Related Parties (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Related Party Transactions [Abstract]
Net accounts receivable, related parties	$ 0.3		$ 0.3		$ 2.0
Accounts payable and accrued expenses, related parties	0.3		0.3		$ 0.4
Joint venture fee income	$ 1.7	$ 1.5	$ 3.3	$ 3.0