Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Assets
Land	$ 967,121	$ 949,777
Buildings and improvements	5,596,754	5,389,674
Real estate assets, at cost, total	6,563,875	6,339,451
Accumulated depreciation	(1,619,325)	(1,518,896)
Net operating real estate assets	4,944,550	4,820,555
Properties under development, including land	438,968	334,463
Investments in joint ventures	43,338	45,092
Properties held for sale	58,765	30,517
Total real estate assets	5,485,621	5,230,627
Accounts receivable - affiliates	27,474	33,625
Other assets, net	112,520	88,260
Cash and cash equivalents	4,707	26,669
Restricted cash	60,889	5,991
Total assets	5,691,211	5,385,172
Liabilities
Unsecured notes payable	1,721,998	1,538,212
Secured notes payable	943,039	972,256
Accounts payable and accrued expenses	124,336	101,896
Accrued real estate taxes	50,247	28,452
Distributions payable	56,793	49,969
Other liabilities	69,716	67,679
Total liabilities	2,966,129	2,758,464
Commitments and contingencies
Non-Qualified deferred compensation share awards	47,092	0
Equity
Common shares of beneficial interest; $0.01 par value per share; 175,000 shares authorized; 99,652 and 99,106 issued; 96,662 and 96,201 outstanding at September 30, 2013 and December 31, 2012, respectively	967	962
Additional paid-in capital	3,595,536	3,587,505
Distributions in excess of net income attributable to common shareholders	(571,935)	(598,951)
Treasury shares, at cost (11,354 and 11,771 common shares at September 30, 2013 and December 31, 2012, respectively)	(410,309)	(425,355)
Accumulated other comprehensive loss	(1,021)	(1,062)
Total common equity	2,613,238	2,563,099
Non-controlling interests	64,752	63,609
Total equity	2,677,990	2,626,708
Total liabilities and equity	$ 5,691,211	$ 5,385,172