Equity Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Balance Sheets:
Real estate properties, net	$ 6,942,072	$ 6,821,803
Acquired real estate leases, net	416,763	427,756
Cash and cash equivalents	48,692	102,219	193,587	192,763
Rents receivable, net	267,733	253,394
Other assets, net	221,790	211,293
Total assets	8,082,668	8,189,634
Unsecured revolving credit facility	135,000	297,000
Mortgage notes payable	980,985	984,827
Assumed real estate lease obligations, net	66,576	69,304
Other liabilities	155,993	194,184
Shareholders' equity	3,728,032	3,105,428
Total liabilities and shareholders' equity	8,082,668	8,189,634
GOV
Balance Sheets:
Real estate properties, net		1,357,986
Acquired real estate leases, net		144,484
Cash and cash equivalents		5,255
Rents receivable, net		29,099
Other assets, net		25,310
Total assets		1,562,134
Unsecured revolving credit facility		49,500
Unsecured term loan		350,000
Mortgage notes payable		93,127
Assumed real estate lease obligations, net		19,129
Other liabilities		22,927
Shareholders' equity		1,027,451
Total liabilities and shareholders' equity		$ 1,562,134