Organization (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Organization [Abstract]
General partner ownership interest (in hundredths)	94.50%
Limited partners ownership interest (in hundredths)	5.50%
Operating Partnership units outstanding (in shares)	2,122,381	2,229,230
Redemption value of Operating Partnership units outstanding	$ 311.2	$ 313.2
Number of apartment communities owned	163
Apartment units owned (in units)	33,468
Ownership interests, number of commercial buildings	5
Ownership interests, number of active development projects	9