Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Real estate properties:
Land	$ 1,458,525	$ 1,339,133
Buildings and improvements	5,785,707	5,018,125
Total real estate properties, at cost, gross	7,244,232	6,357,258
Accumulated depreciation	(934,170)	(850,261)
Total real estate properties, at cost, net	6,310,062	5,506,997
Properties held for sale		114,426
Acquired real estate leases, net	343,917	233,913
Equity investments	177,477	171,464
Cash and cash equivalents	192,763	194,040
Restricted cash	7,869	5,082
Rents receivable, net of allowance for doubtful accounts of $12,575 and $12,550, respectively	217,592	191,237
Other assets, net	197,346	171,380
Total assets	7,447,026	6,588,539
LIABILITIES AND SHAREHOLDERS' EQUITY
Revolving credit facility	100,000
Senior unsecured debt, net	2,845,030	2,854,540
Mortgage notes payable, net	632,301	351,526
Liabilities related to properties held for sale		1,492
Accounts payable and accrued expenses	158,272	123,842
Assumed real estate lease obligations, net	70,179	65,940
Rent collected in advance	37,653	27,988
Security deposits	23,779	22,523
Due to related persons	11,295	8,998
Total liabilities	3,878,509	3,456,849
Commitments and contingencies
Common shares of beneficial interest, $0.01 par value:
Common shares of beneficial interest, $0.01 par value: 350,000,000 shares authorized; 83,721,736 and 72,138,686 shares issued and outstanding, respectively	837	721
Additional paid in capital	3,614,079	3,348,849
Cumulative net income	2,482,321	2,372,337
Cumulative other comprehensive (loss) income	(4,709)	4,706
Cumulative common distributions	(2,826,030)	(2,675,956)
Cumulative preferred distributions	(476,657)	(432,252)
Total shareholders' equity	3,568,517	3,131,690
Total liabilities and shareholders' equity	7,447,026	6,588,539
Series C
50,000,000 shares authorized;
Preferred shares of beneficial interest, $0.01 par value:	145,015	145,015
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