Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Management contracts, initial term	3 years
Management contracts, renewal term	1 year
Notes receivable past due	$ 15.5	$ 12.9
Accounting Standards Update 2016-02 [Member]
Schedule of Equity Method Investments [Line Items]
Lease assets and liabilities recognized, term	12 months