Investments - Schedule of Lease Intangible Assets and Liabilities, Net of Accumulated Amortization (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Capital Leased Assets [Line Items]    
Less: accumulated amortization $ (196,327) $ (187,160)
Intangible lease assets, net 573,925 590,073
Less: accumulated amortization (34,889) (31,625)
Intangible lease liabilities, net 204,161 205,968
In-Place Leases    
Capital Leased Assets [Line Items]    
Intangible lease assets, gross 670,127 676,665
Above-Market Leases    
Capital Leased Assets [Line Items]    
Intangible lease assets, gross 100,125 100,568
Below-Market Leases    
Capital Leased Assets [Line Items]    
Intangible lease liabilities, gross $ 239,050 $ 237,593