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STOCK-BASED COMPENSATION - Stock Appreciation Rights Narrative (Details) - Stock Appreciation Rights (SARs) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock appreciation rights (in shares) 100,000 300,000  
Vesting period 3 years    
Holding period, not less than 1 year    
Exercise period 10 years    
PIPE transaction issuance costs $ 0 $ 0 $ 0