Investments - Narrative (Details)
$ in Millions
Sep. 30, 2019
USD ($)
Property
State
Note
Dec. 31, 2018
Property
Real Estate Properties [Line Items]    
Gross investment in real estate properties and loans | $ $ 5,600.0  
Number of real estate properties | Property 1,666  
Portfolio disbursement, number of states | State 48  
Minimum of investment in real estate properties 10.00%  
Number of properties under operating leases | Property 1,621 1,458
Number of other notes receivable | Note 2  
Number of other notes receivable, secured | Note 1  
Secured Debt    
Real Estate Properties [Line Items]    
Other notes receivable | $ $ 0.1  
Unsecured Debt    
Real Estate Properties [Line Items]    
Other notes receivable | $ $ 1.9  
Financed Real Estate    
Real Estate Properties [Line Items]    
Number of real estate properties | Property 43  
Texas    
Real Estate Properties [Line Items]    
Investment in real estate properties 12.20%