Condensed Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Rental properties:
Land and land improvements	$ 865,321	$ 860,661
Buildings and improvements	3,477,935	3,452,403
Total Rental Properties	4,343,256	4,313,064
Less: accumulated depreciation	(954,243)	(920,026)
Net Real Estate	3,389,013	3,393,038
Real estate under development	45,632	44,280
Co-investments	401,531	383,412
Total Real Estate	3,836,176	3,820,730
Cash and cash equivalents-unrestricted	13,744	12,889
Cash and cash equivalents-restricted	23,603	22,574
Marketable securities	80,000	74,275
Funds held by 1031 exchange facilitator	10,984	0
Notes and other receivables	48,053	66,369
Prepaid expenses and other assets	21,795	22,682
Deferred charges, net	17,023	17,445
Total assets	4,051,378	4,036,964
Liabilities and Equity
Mortgage notes payable	1,724,317	1,745,858
Unsecured debt	465,000	465,000
Lines of credit	153,566	150,000
Accounts payable and accrued liabilities	62,092	48,324
Construction payable	3,337	6,505
Dividends payable	42,096	39,611
Derivative liabilities	2,725	3,061
Other liabilities	20,446	20,528
Total liabilities	2,473,579	2,478,887
Commitments and contingencies
Cumulative convertible preferred stock; $0001 par value:
4875% Series G - 5,890,000 issued, and 178,249 outstanding	4,349	4,349
Equity
Common stock; $.0001 par value, 641,702,178 shares authorized; 34,133,506 and 33,888,082 shares issued and outstanding	3	3
Cumulative redeemable preferred stock at liquidation value	73,750	73,750
Additional paid-in capital	1,877,373	1,844,611
Distributions in excess of accumulated earnings	(422,919)	(408,066)
Accumulated other comprehensive (loss) income	(70,565)	(72,771)
Total stockholders' equity	1,457,642	1,437,527
Noncontrolling interest	115,808	116,201
Total equity	1,573,450	1,553,728
Total liabilities and equity	$ 4,051,378	$ 4,036,964