Basis of Presentation (Details) - property	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Real Estate Properties
Total number of joint venture properties	81	78
Number of joint venture properties managed by the entity	58
Number of International joint venture properties	19
Number of joint venture properties managed by others	23
Ownership interest:
Ownership interest in the Operating Partnership (as a percent)	86.90%	86.90%
Weighted average
Ownership interest:
Ownership interest in the Operating Partnership (as a percent)	86.80%	86.50%	85.60%
Wholly owned properties
Real Estate Properties
Number of properties	134
Partially owned properties
Real Estate Properties
Number of properties	19