Equity Investments (Details2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Balance Sheets:
Real estate properties, net	$ 6,310,062	$ 5,506,997
Acquired real estate leases, net	343,917	233,913
Cash and cash equivalents	192,763	194,040	18,204	15,518
Rents receivable, net	217,592	191,237
Other assets, net	197,346	171,380
Total assets	7,447,026	6,588,539
Revolving credit facility	100,000
Mortgage notes payable	632,301	351,526
Assumed real estate lease obligations, net	70,179	65,940
Other liabilities	158,272	123,842
Shareholders' equity	3,568,517	3,131,690	2,889,066	2,921,112
Total liabilities and shareholders' equity	7,447,026	6,588,539
GOV
Balance Sheets:
Real estate properties, net	1,198,050	846,447
Acquired real estate leases, net	117,596	60,097
Cash and cash equivalents	3,272	2,437
Rents receivable, net	29,000	19,200
Other assets, net	20,657	23,107
Total assets	1,368,575	951,288
Revolving credit facility	345,500	118,000
Mortgage notes payable	95,383	46,428
Assumed real estate lease obligations, net	11,262	13,679
Other liabilities	24,762	15,784
Shareholders' equity	891,668	757,397
Total liabilities and shareholders' equity	$ 1,368,575	$ 951,288