Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Rental properties:
Land and land improvements	$ 1,003,171	$ 860,661
Buildings and improvements	4,030,501	3,452,403
Total Rental Properties	5,033,672	4,313,064
Less: accumulated depreciation	(1,081,517)	(920,026)
Net Real Estate	3,952,155	3,393,038
Real estate under development	66,851	44,280
Co-investments	571,345	383,412
Total Real Estate	4,590,351	3,820,730
Cash and cash equivalents-unrestricted	18,606	12,889
Cash and cash equivalents-restricted	23,520	22,574
Marketable securities	92,713	74,275
Notes and other receivables	66,163	66,369
Prepaid expenses and other assets	35,003	22,682
Deferred charges, net	20,867	17,445
Total assets	4,847,223	4,036,964
Liabilities and Equity
Mortgage notes payable	1,565,599	1,745,858
Unsecured debt	1,112,084	465,000
Lines of credit	141,000	150,000
Accounts payable and accrued liabilities	64,858	48,324
Construction payable	5,392	6,505
Dividends payable	45,052	39,611
Derivative liabilities	6,606	3,061
Other liabilities	22,167	20,528
Total liabilities	2,962,758	2,478,887
Commitments and contingencies
Cumulative convertible preferred stock; $0001 par value:
4.875% Series G - 5,890,000 issued, and 178,249 outstanding	4,349	4,349
Equity:
Common stock; $.0001 par value, 656,020,000 shares authorized;36,442,994 and 33,888,082 shares issued and outstanding	3	3
Cumulative redeemable preferred stock at liquidation value	73,750	73,750
Excess Stock, $.0001 par value, 330,000,000 shares authorized and no shares issued or outstanding	0	0
Additional paid-in capital	2,204,778	1,844,611
Distributions in excess of accumulated earnings	(444,466)	(408,066)
Accumulated other comprehensive loss	(69,261)	(72,771)
Total stockholders' equity	1,764,804	1,437,527
Noncontrolling interest	115,312	116,201
Total equity	1,880,116	1,553,728
Total liabilities and equity	$ 4,847,223	$ 4,036,964