Variable Interest Entities (Narrative) (Details) $ in Millions	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Variable Interest entity, number of entities	2
Investment In Unconsolidated Variable Interest Entities	$ 190.7
Unconsolidated investment maximum exposure to loss	190.7
Long Term Funding Commitment For Project Development	$ 83.0
SVVI [Member]
Number of properties securing unconsolidated variable interest entity	3
Recreation Anchored Lodging [Member]
Number of properties securing unconsolidated variable interest entity	2
Recreation Reportable Operating Segment [Member] | Recreation Anchored Lodging [Member]
Investment In Unconsolidated Variable Interest Entities	$ 30.3	$ 29.5
Unconsolidated investment maximum exposure to loss	$ 30.3
Education Property Member | Education Reportable Operating Segment [Member]
Number of properties securing unconsolidated variable interest entity	1
St. Petersburg Joint Venture [Member]
Long Term Funding Commitment For Project Development	$ 14.6