Equity Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Balance Sheets:
Real estate properties, net	$ 6,821,803	$ 6,310,062
Acquired real estate leases, net	427,756	343,917
Cash and cash equivalents	102,219	192,763	194,040	18,204
Rents receivable, net	253,394	217,592
Other assets, net	211,293	197,346
Total assets	8,189,634	7,447,026
Unsecured revolving credit facility	297,000	100,000
Mortgage notes payable	984,827	632,301
Assumed real estate lease obligations, net	69,304	70,179
Other liabilities	194,184	158,272
Shareholders' equity	3,105,428	3,568,517
Total liabilities and shareholders' equity	8,189,634	7,447,026
GOV
Balance Sheets:
Real estate properties, net	1,357,986	1,198,050
Acquired real estate leases, net	144,484	117,596
Cash and cash equivalents	5,255	3,272
Rents receivable, net	29,099	29,000
Other assets, net	25,310	20,657
Total assets	1,562,134	1,368,575
Unsecured revolving credit facility	49,500	345,500
Unsecured term loan	350,000
Mortgage notes payable	93,127	95,383
Assumed real estate lease obligations, net	19,129	11,262
Other liabilities	22,927	24,762
Shareholders' equity	1,027,451	891,668
Total liabilities and shareholders' equity	$ 1,562,134	$ 1,368,575