Quarterly report pursuant to Section 13 or 15(d)

DEBT FINANCING - Debt Summary (Details)

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DEBT FINANCING - Debt Summary (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Sep. 30, 2016
Debt Instrument [Line Items]      
Total principal $ 1,068,678 $ 873,194  
Unamortized debt issuance costs and debt premium, net 3,176 5,760  
Total debt $ 1,071,854 878,954  
Line of Credit [Member] | Credit Facility [Member] | Revolving line of credit [Member]      
Debt Instrument [Line Items]      
Effective interest rate (percent) 2.63%   1.93%
Total principal $ 201,000 246,500  
Unsecured Debt [Member] | Credit Facility [Member] | Tranche A Term Loan [Member]      
Debt Instrument [Line Items]      
Effective interest rate (percent) 2.63%    
Total principal $ 235,000 225,000  
Unsecured Debt [Member] | Credit Facility [Member] | Tranche B Term Loan [Member]      
Debt Instrument [Line Items]      
Effective interest rate (percent) 3.24%    
Total principal $ 155,000 100,000  
Unsecured Debt [Member] | Credit Facility [Member] | Tranche C Term Loan [Member]      
Debt Instrument [Line Items]      
Effective interest rate (percent) 3.71%    
Total principal $ 105,000 0  
Unsecured Debt [Member] | Term Loan Facility [Member]      
Debt Instrument [Line Items]      
Effective interest rate (percent) 3.08%    
Total principal $ 100,000 100,000  
Mortgages [Member] | Fixed Rate Mortgages [Member]      
Debt Instrument [Line Items]      
Effective interest rate (percent) 4.15%    
Total principal $ 272,678 $ 201,694