Annual report pursuant to Section 13 and 15(d)

Mortgage Notes Payable, Revolving Credit Facility, and Term Loan Facility - Mortgage Notes Payable (Details)

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Mortgage Notes Payable, Revolving Credit Facility, and Term Loan Facility - Mortgage Notes Payable (Details)
$ in Thousands
12 Months Ended
Oct. 27, 2017
Dec. 31, 2018
USD ($)
property
Dec. 31, 2017
USD ($)
property
Dec. 31, 2016
USD ($)
Sep. 30, 2018
Debt Instrument [Line Items]          
Debt repaid   $ 27,850 $ 60,080 $ 88,899  
Weighted Average Interest Rate on Fixed Rate Debt Extended   4.59%      
Number of properties acquired | property   5 7    
Fixed rate mortgage loans          
Debt Instrument [Line Items]          
Debt repaid   $ 9,444      
Stated interest rate (as a percent)   5.75%      
Variable rate mortgage loans          
Debt Instrument [Line Items]          
Debt repaid   $ 6,738      
New fixed rate mortgage notes payable          
Debt Instrument [Line Items]          
Aggregate Fixed Rate Debt Issued or Assumed   $ 21,043      
Number of properties acquired in connection with fixed rate | property   2      
Number of properties acquired | property   5      
Stated interest rate (as a percent)   4.76%      
Fixed rate mortgage loans debt extended          
Debt Instrument [Line Items]          
Aggregate Fixed Rate Debt Extended   $ 3,598      
Weighted Average Interest Rate on Fixed Rate Debt Extended   4.92%      
Debt instrument term   3 years      
Variable rate mortgage loans debt extended          
Debt Instrument [Line Items]          
Aggregate Fixed Rate Debt Issued or Assumed   $ 24,832      
Debt instrument term   1 year 6 months 8 days      
LIBOR          
Debt Instrument [Line Items]          
Interest Rate on Variable Rate Debt Repaid 2.75%        
LIBOR | Variable rate mortgage loans | Weighted Average          
Debt Instrument [Line Items]          
Interest Rate on Variable Rate Debt Repaid   2.25%      
LIBOR | Variable rate mortgage loans debt extended | Weighted Average          
Debt Instrument [Line Items]          
Interest Rate on Variable Rate Debt Repaid   2.29027%      
Interest rate swaps | New fixed rate mortgage notes payable          
Debt Instrument [Line Items]          
Number of interest rate swaps | property   2      
Interest rate swap one | New fixed rate mortgage notes payable          
Debt Instrument [Line Items]          
Stated interest rate (as a percent)         4.58%
Interest rate swap two | New fixed rate mortgage notes payable          
Debt Instrument [Line Items]          
Stated interest rate (as a percent)   5.32%      
Detroit, Michigan | Interest rate swaps | New fixed rate mortgage notes payable          
Debt Instrument [Line Items]          
Stated interest rate (as a percent)   4.625%