v3.8.0.1
UNIT-BASED COMPENSATION Table 3 - Summary of Performance Units (Details) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Unit-based awards, beginning balance (units) 793,097  
Unit-based awards, ending balance (units) 902,911 793,097
Performance Units [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Performance units awarded and outstanding, period start 77,014  
Performance units awarded 39,320  
Performance units awarded and outstanding, period end 80,961 77,014
Unit-based awards, beginning balance (units) 35,373  
Unit-based awards, granted (units) 38,865 0
Unit-based awards, vested (units) (35,373)  
Unit-based awards, ending balance (units) 38,865 35,373
Weighted-average grant date fair value, period start $ 31.75  
Weighted-average grant date fair value, granted 50.04  
Weighted-average grant date fair value, vested 31.75  
Weighted-average grant date fair value, period end $ 50.04 $ 31.75