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DEBT (Details)
$ in Thousands
12 Months Ended
Dec. 31, 2018
USD ($)
extension
Oct. 31, 2012
USD ($)
Debt Instrument Variable Rate Base US Federal Funds [Member]    
Short-term Debt [Line Items]    
Basis spread on variable rate (as a percent) 0.50%  
Debt Instrument Variable Rate Base Adjusted LIBOR [Member]    
Short-term Debt [Line Items]    
Basis spread on variable rate (as a percent) 1.00%  
Eurodollar Loans, Adjusted LIBOR Rate [Member]    
Short-term Debt [Line Items]    
Basis spread on variable rate (as a percent) 0.75%  
Unsecured Line of Credit Facility [Member]    
Short-term Debt [Line Items]    
Maximum borrowing capacity   $ 175,000
Number of anniversaries for optional annual extensions of the credit agreement | extension 3  
Period of extension 1 year  
Amount outstanding $ 0  
Number of options available for calculating variable interest rate | extension 2  
Letter of Credit [Member]    
Short-term Debt [Line Items]    
Maximum borrowing capacity   75,000
Letter of credit amount maintained $ 32,900  
Swingline Credit Facility [Member]    
Short-term Debt [Line Items]    
Maximum borrowing capacity   $ 25,000
Amount outstanding $ 0  
Minimum [Member] | Eurodollar Loans, Adjusted LIBOR Rate [Member]    
Short-term Debt [Line Items]    
Basis spread on variable rate (as a percent) 0.75%  
Maximum [Member] | Eurodollar Loans, Adjusted LIBOR Rate [Member]    
Short-term Debt [Line Items]    
Basis spread on variable rate (as a percent) 1.00%