Condensed Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Rental properties:
Land and land improvements	$ 1,054,178	$ 1,003,171
Buildings and improvements	4,194,092	4,030,501
Total Rental Properties	5,248,270	5,033,672
Less accumulated depreciation	(1,173,333)	(1,081,517)
Net Real Estate	4,074,937	3,952,155
Real estate under development	70,242	66,851
Co-investments	618,259	571,345
Total Real Estate	4,763,438	4,590,351
Cash and cash equivalents-unrestricted	20,217	18,606
Cash and cash equivalents-restricted	25,167	23,520
Marketable securities	88,734	92,713
Notes and other receivables	110,544	66,163
Prepaid expenses and other assets	27,890	35,003
Deferred charges, net	23,008	20,867
Total assets	5,058,998	4,847,223
Liabilities and Equity
Mortgage notes payable	1,511,502	1,565,599
Unsecured debt	1,409,744	1,112,084
Lines of credit	4,370	141,000
Accounts payable and accrued liabilities	76,410	64,858
Construction payable	7,731	5,392
Dividends payable	50,488	45,052
Derivative liabilities	1,928	6,606
Other liabilities	22,432	22,167
Total liabilities	3,084,605	2,962,758
Commitments and contingencies
Cumulative convertible Series G preferred stock	4,349	4,349
Equity:
Cumulative redeemable Series H preferred stock at liquidation value	73,750	73,750
Common stock, $.0001 par value, 656,020,000 shares authorized 37,317,622 and 36,442,994 shares issued and outstanding	3	3
Additional paid-in capital	2,331,830	2,204,778
Distributions in excess of accumulated earnings	(484,615)	(444,466)
Accumulated other comprehensive loss, net	(62,813)	(69,261)
Total stockholders' equity	1,858,155	1,764,804
Noncontrolling interest	111,889	115,312
Total equity	1,970,044	1,880,116
Total liabilities and equity	$ 5,058,998	$ 4,847,223