Basis of Presentation (Details)	6 Months Ended
	Jun. 30, 2012 property	Jun. 30, 2011	Dec. 31, 2011
Properties:
Wholly owned properties included in consolidation	228
Partially owned properties included in consolidation	18
Total number of joint venture properties	91
Number of joint venture properties managed by the entity	77
Number of International joint venture properties	12
Number of joint venture properties managed by others	14
Ownership interest:
Weighted average ownership percentage in the Operating Partnership	83.10%	83.00%
Ownership percentage in the Operating Partnership	83.30%		82.80%