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STOCK-BASED COMPENSATION - Additional Information - Stock Options (Details) - Stock option plans - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
STOCK OPTION PLANS      
Number of shares underlying options exercisable 127,122    
Number of shares underlying options unvested 133,200    
Number of shares underlying options outstanding 260,322    
Weighted-average exercise price per share exercisable $ 12.49    
Weighted-average exercise price per share unvested 19.36    
Weighted-average exercise price per share outstanding $ 16.00 $ 12.80 $ 10.99
Aggregate intrinsic value exercisable $ 2,183,000    
Aggregate intrinsic value unvested 1,372,000    
Aggregate intrinsic value outstanding $ 3,555,000    
Weighted-average contractual term exercisable (years) 4 years 6 months    
Weighted-average contractual term unvested (years) 8 years 7 months 6 days    
Weighted-average contractual term outstanding (years) 6 years 7 months 6 days    
Intrinsic value of options exercised $ 118,000 $ 2,800,000 $ 160,000