Investments - Summary of Owned Real Estate Activity (Footnote) (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Dec. 31, 2019
Real Estate [Line Items]          
Revenue producing capitalized expenditures     $ 7,600    
Capitalized maintenance expenditures     2,400    
Impairments on owned real estate $ 21,272 $ 3,607 61,436 $ 7,299  
Allowance for credit losses on direct financing leases 0 $ 0 304 $ 0  
Operating lease held in use land and buildings, net 5,102,347   5,102,347    
Intangible lease assets, net 350,466   350,466   $ 385,079
Real estate assets under direct financing leases, net 7,300   7,300   14,465
Real estate assets held for sale, net 12,708   12,708   1,144
Intangible lease liabilities, net (120,934)   (120,934)   $ (127,335)
Net balance $ 5,351,887   5,351,887    
Held-in-use          
Real Estate [Line Items]          
Gain on disposal of assets for properties     1,100    
Held-for-sale          
Real Estate [Line Items]          
Gain on disposal of assets for properties     $ 100