Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Assets
Land	$ 997,349	$ 969,711
Buildings and improvements	5,894,453	5,629,904
Real estate assets, at cost, total	6,891,802	6,599,615
Accumulated depreciation	(1,813,124)	(1,643,713)
Net operating real estate assets	5,078,678	4,955,902
Properties under development, including land	576,269	472,566
Investments in joint ventures	35,180	42,155
Total real estate assets	5,690,127	5,470,623
Accounts receivable – affiliates	25,954	27,724
Other assets, net	123,999	109,401
Cash and cash equivalents	66,127	17,794
Restricted cash	5,769	6,599
Total assets	5,911,976	5,632,141
Liabilities
Unsecured notes payable	1,837,621	1,588,798
Secured notes payable	906,328	941,968
Accounts payable and accrued expenses	147,255	113,307
Accrued real estate taxes	54,369	35,648
Distributions payable	60,265	56,787
Other liabilities	94,230	88,272
Total liabilities	3,100,068	2,824,780
Commitments and contingencies
Non-qualified deferred compensation share awards	60,363	47,180
Equity
Common shares of beneficial interest; $0.01 par value per share; 175,000 shares authorized; 100,413 and 99,645 issued; 97,386 and 96,660 outstanding at September 30, 2014 and December 31, 2013, respectively	974	967
Additional paid-in capital	3,649,750	3,596,069
Distributions in excess of net income attributable to common shareholders	(568,142)	(494,167)
Treasury shares, at cost (11,000 and 11,352 common shares at September 30, 2014 and December 31, 2013, respectively)	(397,497)	(410,227)
Accumulated other comprehensive loss	(1,474)	(1,106)
Total common equity	2,683,611	2,691,536
Non-controlling interests	67,934	68,645
Total equity	2,751,545	2,760,181
Total liabilities and equity	$ 5,911,976	$ 5,632,141