Equity Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010
Balance Sheets:
Real estate properties, net	$ 6,636,368	$ 6,310,062
Acquired real estate leases, net	364,282	343,917
Cash and cash equivalents	138,805	192,763	55,035	194,040
Rents receivable, net	236,001	217,592
Other assets, net	228,562	197,346
Total assets	7,798,584	7,447,026
Unsecured revolving credit facility		100,000
Mortgage notes payable	801,709	632,301
Assumed real estate lease obligations, net	69,237	70,179
Other liabilities	158,044	158,272
Shareholders' equity	3,472,041	3,568,517
Total liabilities and shareholders' equity	7,798,584	7,447,026
GOV
Balance Sheets:
Real estate properties, net	1,211,295	1,198,050
Acquired real estate leases, net	110,805	117,596
Cash and cash equivalents	1,394	3,272
Rents receivable, net	27,086	29,000
Other assets, net	32,244	20,657
Total assets	1,382,824	1,368,575
Unsecured revolving credit facility	27,000	345,500
Unsecured term loan	350,000
Mortgage notes payable	94,271	95,383
Assumed real estate lease obligations, net	10,721	11,262
Other liabilities	22,530	24,762
Shareholders' equity	878,302	891,668
Total liabilities and shareholders' equity	$ 1,382,824	$ 1,368,575