Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Assets
Land	$ 949,777	$ 768,016
Buildings and improvements	5,389,674	4,751,654
Real estate assets, at cost, total	6,339,451	5,519,670
Accumulated depreciation	(1,518,896)	(1,432,799)
Net operating real estate assets	4,820,555	4,086,871
Properties under development, including land	334,463	299,870
Investments in joint ventures	45,092	44,844
Properties held for sale	30,517	11,131
Total real estate assets	5,230,627	4,442,716
Accounts receivable - affiliates	33,625	31,035
Other assets, net	88,260	88,089
Cash and cash equivalents	26,669	55,159
Restricted cash	5,991	5,076
Total assets	5,385,172	4,622,075
Liabilities
Unsecured notes payable	1,538,212	1,380,755
Secured notes payable	972,256	1,051,357
Accounts payable and accrued expenses	101,896	93,747
Accrued real estate taxes	28,452	21,883
Distributions payable	49,969	39,364
Other liabilities	67,679	109,276
Total liabilities	2,758,464	2,696,382
Commitments and contingencies
Perpetual preferred units	0	97,925
Equity
Common shares of beneficial interest; $0.01 par value per share; 175,000 and 100,000 shares authorized; 99,106 and 87,377 issued; 96,201 and 84,517 outstanding at December 31, 2012 and December 31, 2011, respectively	962	845
Additional paid-in capital	3,587,505	2,901,024
Distributions in excess of net income attributable to common shareholders	(598,951)	(690,466)
Treasury shares, at cost (11,771 and 12,509 common shares at December 31, 2012 and December 31, 2011, respectively)	(425,355)	(452,003)
Accumulated other comprehensive loss	(1,062)	(683)
Total common equity	2,563,099	1,758,717
Non-controlling interests	63,609	69,051
Total equity	2,626,708	1,827,768
Total liabilities and equity	$ 5,385,172	$ 4,622,075