Net Lease Assets, net (Details) (USD $)	1 Months Ended	3 Months Ended		6 Months Ended
	Apr. 30, 2012 LeaseAssets	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Net Lease Assets
Less: accumulated depreciation		$ (342,233,000)		$ (342,233,000)		$ (346,316,000)
Net lease assets, net		1,550,113,000		1,550,113,000		1,702,764,000
Sale of portfolio leased assets (in lease assets)	12
Property subject to or available for operating lease sold, aggregate, carrying value	105,700,000			9,800,000
Net gain on sale of net lease assets	24,900,000			2,400,000
Impairment charges on net lease assets		6,200,000		20,200,000
Impairment charges on net lease assets recorded in income (loss) from discontinued operations				500,000
Customer expense reimbursements		5,900,000	6,000,000	11,400,000	11,500,000
Allowance for doubtful accounts related to tenant receivables including deferred operating lease income receivable		4,400,000		4,400,000		3,700,000
Facilities and improvements
Net Lease Assets
Net lease assets, gross		1,480,678,000		1,480,678,000		1,601,477,000
Land and land improvements
Net Lease Assets
Net lease assets, gross		411,668,000		411,668,000		447,603,000
Secured Term Loan LIBOR plus 4.50% due 2014
Net Lease Assets
Repayment of principal amount	$ 50,800,000