Basis of Presentation (Details)	3 Months Ended
	Mar. 31, 2013 property	Mar. 31, 2012	Dec. 31, 2012
Properties:
Wholly owned properties included in consolidation	220
Partially owned properties included in consolidation	18
Total number of joint venture properties	87
Number of joint venture properties managed by the entity	71
Number of International joint venture properties	12
Number of joint venture properties managed by others	16
Ownership interest:
Weighted average ownership percentage in the Operating Partnership	85.60%	82.90%
Ownership percentage in the Operating Partnership	85.60%		85.60%