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EMPLOYEE STOCK COMPENSATION - SARs Weighted Average Fair Value Assumptions (Details) - Stock appreciation rights - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield 0.00% 0.00% 0.00%
Expected volatility 0.00% 0.00% 23.79%
Expected term 0 years 0 years 2 years 7 days
Risk-free interest rate 0.00% 0.00% 0.64%
Fair value per share (in dollars per share) $ 0.00 $ 0.00 $ 1.72