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INCENTIVE PLANS - Stock Option Activity (Details) - $ / shares
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Options (in shares):        
Outstanding, beginning of period (in shares) 762,225 1,138,813 1,527,396  
Canceled (in shares) (11,365) 0 0  
Expired (in shares) (449,916) (376,588) 0  
Exercised (in shares) (134,294) 0 (388,583)  
Outstanding, end of period (in shares) 166,650 762,225 1,138,813  
Exercisable, end of period (in shares) 166,650 762,225 1,138,813  
Weighted- average exercise price (in dollars per share):        
Outstanding, beginning of period (in dollars per share) $ 101.84 $ 161.96 $ 131.78  
Canceled (in dollars per share) 40.80 0 0  
Expired (in dollars per share) 142.30 283.63 0  
Exercised (in dollars per share) 39.00 0 43.35  
Outstanding, end of period (in dollars per share) 47.42 101.84 161.96  
Intrinsic value per share (in dollars per share):        
Outstanding (in dollars per share) 32.47 0 0 $ 0
Exercised (in dollars per share) $ 23.50 $ 0 $ 15.67