Investments - Summary of Real Estate and Loan Activity, Net of Accumulated Depreciation and Amortization (Footnote) (Details)
$ in Millions
3 Months Ended
Mar. 31, 2015
USD ($)
Property
Dec. 31, 2014
Property
Real Estate Properties [Line Items]    
Revenue producing capitalized expenditures $ 0.2  
Capitalized maintenance expenditures 0.2  
Accumulated depreciation and amortization associated with dispositions of real estate $ 12.5  
Number of properties sold under 1031 Exchanges | Property 6  
Amount of properties sold under 1031 Exchanges $ 39.4  
Amount of properties acquired under 1031 Exchanges $ (32.5)  
Number of properties acquired under 1031 Exchanges | Property 4  
Properties Vacant    
Real Estate Properties [Line Items]    
Number of properties | Property 42 37
Property Held For Sale    
Real Estate Properties [Line Items]    
Number of properties | Property 14 8