Basis of Presentation - Narratives (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) vie	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) vie
Basis of Consolidation
Variable interest entities, count	29		28
Variable interest entities consolidated, count	22		21
Variable interest entities unconsolidated, count	7		7
Variable interest entity, maximum exposure to loss | $	$ 153,400		$ 152,700
Operating property revenues | $	$ 7,218	$ 6,980
Owned Real Estate
Basis of Consolidation
Variable interest entities unconsolidated, count	6		6
Managed Programs
Basis of Consolidation
Variable interest entities unconsolidated, count	1