Real Estate Disposition Activities (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Real estate disposition activities
Gain on sale of real estate assets	$ 33,682,000	$ 95,049,000	$ 118,173,000	$ 95,049,000
Summary of income from discontinued operations
Rental income	897,000	9,425,000	5,890,000	19,537,000
Operating and other expenses	(314,000)	(3,088,000)	(1,621,000)	(6,314,000)
Interest expense, net		(55,000)		(138,000)
Loss on extinguishment of debt		(602,000)		(602,000)
Depreciation expense	(220,000)	(1,795,000)	(875,000)	(4,194,000)
Income from discontinued operations	363,000	3,885,000	3,394,000	8,289,000
Avalon Dublin Station I
Real estate disposition activities
Apartment homes	305
Proceeds from sale of real estate	105,400,000
Gain on sale of real estate assets	$ 33,682,000