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DEBT (Senior Unsecured Revolving Credit Facility) (Narrative) (Details) - Unsecured Senior Revolving Credit Facility [Member] - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Debt Instrument [Line Items]    
Credit facility capacity $ 750,000,000  
Amount outstanding $ 0 $ 0
Minimum [Member]    
Debt Instrument [Line Items]    
Interest rate in excess of LIBOR 0.75%  
Maximum [Member]    
Debt Instrument [Line Items]    
Interest rate in excess of LIBOR 1.63%  
LIBOR [Member]    
Debt Instrument [Line Items]    
Interest rate in excess of LIBOR 1.125% 1.125%
Letter of Credit [Member]    
Debt Instrument [Line Items]    
Credit facility capacity $ 150,000,000