Supplemental Cash Flow Disclosures (Details) (USD $)
In Thousands, unless otherwise specified
6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Dec. 31, 2011
Supplemental Disclosures of Non-Cash Investing and Financing Activitie [Abstract]      
Distributions declared and unpaid $ 10,766 $ 10,772 $ 11,157
Common stock issued through distribution reinvestment plan offering 28,974 29,947  
Net unrealized loss on marketable securities 0 (1,713)  
Reclassification of unrealized gain on marketable securities into net income 0 14,654  
Net unrealized gain (loss) on interest rate swaps 788 (697)  
Accrued capital expenditures 1,138 57  
Accrued deferred financing costs 139 0  
Supplemental Cash Flow Disclosures [Abstract]      
Interest paid $ 49,803 $ 49,085