Investments - Narrative (Details) (USD $)
9 Months Ended
Sep. 30, 2014
Property
State
Dec. 31, 2013
Property
Investment [Line Items]    
Real estate properties and loans, gross $ 7,705,490,000 [1] $ 7,235,732,000 [1]
Real estate assets held for sale 2,408 2,186
Properties dispersed geographically 49  
Minimum percentage of investment in real estate properties 10.00%  
Number of owned real estate properties 2,263 2,041
Securing mortgage properties 145 145
Securing mortgage properties carrying amount 111,000,000 117,300,000
Other loan receivable with aggregate carrying value 400,000 400,000
Accumulated depreciation and amortization associated with dispositions of real estate 6,700,000  
Number of real estate properties held for sale 20 [2] 11
Properties Vacant
   
Investment [Line Items]    
Number of properties 40 21
Property Held For Sale
   
Investment [Line Items]    
Number of properties 7 6
Texas
   
Investment [Line Items]    
Number of states exceeding disclosure threshold 1  
Percentage of investment in real estate properties 12.90%  
Continuing operations
   
Investment [Line Items]    
Number of real estate properties held for sale 15  
Rental properties $ 44,600,000  
[1] The dollar amount of investments includes the gross investment in land, buildings and lease intangibles, as adjusted for any impairment, related to properties owned and the carrying amount of loans receivable and real estate assets held under direct financing leases.
[2] Includes fifteen properties with a net carrying amount of $44.6 million in which its operating results are reported in continuing operations.