Debt - CMBS - Narrative (Details)
$ in Thousands
6 Months Ended
Jan. 22, 2018
USD ($)
Jun. 30, 2018
USD ($)
Property
loan
Jun. 30, 2018
USD ($)
Property
loan
Jun. 30, 2018
USD ($)
Property
loan
Loan
Jun. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
Debt Instrument [Line Items]            
Weighted average stated interest rate, excluding defaulted loans   5.35% 5.35% 5.35%    
Capitalized interest [1]   $ 412     $ 1,206  
CMBS Loans            
Debt Instrument [Line Items]            
Unamortized deferred financing costs   3,500 $ 3,500 $ 3,500   $ 3,900
Unamortized discount   $ 100 $ 100 $ 100   $ 100
CMBS Loans | CMBS            
Debt Instrument [Line Items]            
Number of loans secured by mortgage on leased properties and related assets | loan   6 6 6    
Number of properties securing borrowings | Property   100 100 100    
Number of properties securing loans | Property   1 1 1    
Default interest rate   9.85% 9.85% 9.85%    
Debt default amount   $ 9,600 $ 9,600 $ 9,600    
Capitalized interest   $ 2,900        
CMBS Loans | CMBS | Minimum            
Debt Instrument [Line Items]            
Stated interest rate   4.67% 4.67% 4.67%    
CMBS Loans | CMBS | Maximum            
Debt Instrument [Line Items]            
Stated interest rate   6.00% 6.00% 6.00%    
Discontinued Operations, Disposed of by Sale | CMBS Loans            
Debt Instrument [Line Items]            
Number of loans in default     1 1    
Societe Generale And Barclays Bank PLC | Non-Recourse CMBS Loan Agreement | Loans Payable            
Debt Instrument [Line Items]            
Maturity 10 years          
Proceeds from issuance of debt $ 84,000          
10-year Mid-Market Swap Rate | Societe Generale And Barclays Bank PLC | Non-Recourse CMBS Loan Agreement | Loans Payable            
Debt Instrument [Line Items]            
Basis spread on variable rate 2.45%          
[1] Accrued and overdue interest on certain CMBS notes that have been intentionally placed in default.