Significant Transactions - Acquisitions of Noncontrolling Interests in Consolidated Real Estate Partnerships (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 Property PartnershipUnit	Dec. 31, 2012 PartnershipUnit Property
Acquisitions of Noncontrolling Interests in Consolidated Real Estate Partnerships [Abstract]
Consolidated partnerships in which remaining limited partnership interests were acquired	$ 17,900	$ 50,654
Cost of limited partnership interests acquired	5	17
Number of apartment communities owned by partnerships	3	11
Excess of consideration paid over the carrying amount of noncontrolling interests acquired	$ 17,170	$ 44,777