CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Real estate properties:
Land	$ 747,181	$ 699,135
Buildings and improvements	5,168,335	4,838,030
Total real estate properties, at cost, gross	5,915,516	5,537,165
Accumulated depreciation	(934,776)	(895,059)
Total real estate properties, at cost, net	4,980,740	4,642,106
Properties held for sale	214,677	573,531
Acquired real estate leases, net	244,634	255,812
Equity investments	518,934	517,991
Cash and cash equivalents	177,555	222,449
Restricted cash	17,441	22,101
Rents receivable, net of allowance for doubtful accounts of $7,462 and $7,885, respectively	239,766	223,769
Other assets, net	206,967	188,675
Total assets	6,600,714	6,646,434
LIABILITIES AND SHAREHOLDERS' EQUITY
Revolving credit facility	235,000	235,000
Senior unsecured debt, net	1,856,135	1,855,900
Mortgage notes payable, net	898,804	914,510
Liabilities related to properties held for sale	23,066	28,734
Accounts payable and accrued expenses	136,482	165,855
Assumed real estate lease obligations, net	33,064	33,935
Rent collected in advance	29,618	27,553
Security deposits	13,682	11,976
Due to related persons	15,793	9,385
Total liabilities	3,241,644	3,282,848
Common shares of beneficial interest, $0.01 par value:
Common shares of beneficial interest, $0.01 par value: 350,000,000 shares authorized; 118,413,730 and 118,386,918 shares issued and outstanding, respectively	1,184	1,184
Additional paid in capital	4,217,651	4,213,474
Cumulative net income	2,230,288	2,209,840
Cumulative other comprehensive loss	(26,724)	(38,331)
Cumulative common distributions	(3,111,868)	(3,082,271)
Cumulative preferred distributions	(585,122)	(573,971)
Total shareholders' equity	3,359,070	3,363,586
Total liabilities and shareholders' equity	6,600,714	6,646,434
Series D
50,000,000 shares authorized;
Preferred shares of beneficial interest, $0.01 par value	368,270	368,270
Series E
50,000,000 shares authorized;
Preferred shares of beneficial interest, $0.01 par value	$ 265,391	$ 265,391