Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Assets
Land	$ 978,770	$ 969,711
Buildings and improvements	5,691,619	5,629,904
Real estate assets, at cost, total	6,670,389	6,599,615
Accumulated depreciation	(1,698,724)	(1,643,713)
Net operating real estate assets	4,971,665	4,955,902
Properties under development, including land	515,141	472,566
Investments in joint ventures	36,719	42,155
Total real estate assets	5,523,525	5,470,623
Accounts receivable – affiliates	26,145	27,724
Other assets, net	107,862	109,401
Cash and cash equivalents	16,768	17,794
Restricted cash	5,549	6,599
Total assets	5,679,849	5,632,141
Liabilities
Unsecured notes payable	1,649,041	1,588,798
Secured notes payable	940,881	941,968
Accounts payable and accrued expenses	124,981	113,307
Accrued real estate taxes	21,922	35,648
Distributions payable	59,728	56,787
Other liabilities	88,693	88,272
Total liabilities	2,885,246	2,824,780
Commitments and contingencies
Non-qualified deferred compensation share awards	55,498	47,180
Equity
Common shares of beneficial interest; $0.01 par value per share; 175,000 shares authorized; 99,698 and 99,645 issued; 96,623 and 96,660 outstanding at March 31, 2014 and December 31, 2013, respectively	966	967
Additional paid-in capital	3,593,633	3,596,069
Distributions in excess of net income attributable to common shareholders	(523,321)	(494,167)
Treasury shares, at cost (11,055 and 11,352 common shares at March 31, 2014 and December 31, 2013, respectively)	(399,510)	(410,227)
Accumulated other comprehensive loss	(1,091)	(1,106)
Total common equity	2,670,677	2,691,536
Non-controlling interests	68,428	68,645
Total equity	2,739,105	2,760,181
Total liabilities and equity	$ 5,679,849	$ 5,632,141