REVOLVING CREDIT FACILITY AND UNSECURED TERM LOANS (Details)
 9 Months Ended
Apr. 06, 2017
USD ($)
Apr. 04, 2017
USD ($)
Oct. 26, 2015
USD ($)
Dec. 17, 2013
USD ($)
Jun. 20, 2011
USD ($)
Sep. 30, 2017
USD ($)
Dec. 31, 2016
USD ($)
Apr. 22, 2015
USD ($)
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS                
Loan procurement costs, net of amortization           $ 1,709,000 $ 2,150,000  
Unsecured term loan           299,295,000 398,749,000  
Less: Loan procurement costs, net           (1,709,000) (2,150,000)  
Term Loan B                
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS                
Unsecured term loan           $ 100,000,000 100,000,000  
Effective interest rate (as a percent)           3.62%    
Term Loan Facility | Maximum                
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS                
Total indebtedness to total asset value ratio (as a percent)           60.00%    
Percentage of funds from operations that can be distributed on common shares           95.00%    
Term Loan Facility | Term Loan A                
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS                
Maximum borrowing capacity         $ 100,000,000      
Term of debt instrument         5 years      
Write off of unamortized cost $ 200,000              
Variable interest rate basis           LIBOR    
Repayment of outstanding debt $ 100,000,000              
Unsecured term loan             100,000,000  
Term Loan Facility | Term Loan A | Baa2/BBB                
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS                
Interest rate, basis spread (as a percent)           1.30%    
Term Loan Facility | Term Loan B                
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS                
Maximum borrowing capacity         $ 100,000,000      
Term of debt instrument         7 years      
Variable interest rate basis           LIBOR    
Term Loan Facility | Term Loan B | Baa2/BBB                
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS                
Interest rate, basis spread (as a percent)           1.15%    
Credit Facility                
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS                
Loan procurement costs, net of amortization           $ 705,000 1,251,000  
Unsecured term loan           300,000,000 400,000,000  
Less: Loan procurement costs, net           (705,000) (1,251,000)  
Total unsecured term loans, net           $ 299,295,000 398,749,000  
Effective weighted average interest rate (as a percent)           2.82%    
Tangible net worth           $ 821,211,200    
Net proceeds from equity issuances added to minimum tangible net worth (as a percent)           75.00%    
Credit Facility | Minimum                
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS                
Fixed charge coverage ratio           1.50    
Credit Facility | Maximum                
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS                
Total indebtedness to total asset value ratio (as a percent)           60.00%    
Percentage of funds from operations that can be distributed on common shares           95.00%    
Credit Facility | Revolver                
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS                
Maximum borrowing capacity               $ 500,000,000
Interest rate, basis spread (as a percent)           1.25%    
Facility fee (as a percent)           0.15%    
Remaining borrowing capacity           $ 432,600,000    
Outstanding letter of credit           700,000    
Credit Facility | Unsecured term loan                
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS                
Unsecured term loan           $ 200,000,000 $ 200,000,000  
Effective interest rate (as a percent)           2.53%    
Senior notes 4.375% due 2023                
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS                
Proceeds from senior notes   $ 50,000,000   $ 250,000,000        
Interest rate (as a percent)   4.375%   4.375%   4.375%    
Effective interest rate (as a percent)   3.495%   4.501%   4.33%    
Effective weighted average interest rate (as a percent)           4.33%    
Senior notes 4.000% due 2025                
SECURED CREDIT FACILITY, UNSECURED CREDIT FACILITY AND SECURED TERM LOANS                
Proceeds from senior notes   $ 50,000,000 $ 250,000,000          
Interest rate (as a percent)   4.00% 4.00%     4.00%    
Effective interest rate (as a percent)   3.811% 4.032%     3.99%    
Effective weighted average interest rate (as a percent)           3.994%