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STOCK-BASED COMPENSATION - Additional Information - Restricted stock (Details) - USD ($)
1 Months Ended 12 Months Ended
Nov. 30, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
STOCK OPTION PLANS AND RESTRICTED STOCK        
Compensation expense   $ 329,000 $ 43,000 $ 12,000
Unrecognized compensation expense   $ 6,200,000    
Weighted average period   3 years 1 month 6 days    
Restricted Stock        
STOCK OPTION PLANS AND RESTRICTED STOCK        
Number of shares underlying restricted stock unvested   212,580    
Number of shares underlying restricted stock outstanding   212,580    
Weighted-average grant date fair value per share unvested   $ 27.27    
Weighted-average grant date fair value per share unvested outstanding   $ 27.27    
Aggregate grant date fair value unvested   $ 5,797,000    
Aggregate grant date fair value outstanding   $ 5,797,000    
Weighted-average contractual term unvested (years)   4 years 4 months 24 days    
Weighted-average contractual term outstanding (years)   4 years 4 months 24 days    
Directors, executive officers and key employees | 2017 Plan | Restricted Stock        
STOCK OPTION PLANS AND RESTRICTED STOCK        
Number of shares of restricted stock granted 212,580      
Accrued dividends payable   $ 11,000    
Directors | 2017 Plan | Restricted Stock        
STOCK OPTION PLANS AND RESTRICTED STOCK        
Vesting period 2 years      
Executive officers and employees | 2017 Plan | Restricted Stock        
STOCK OPTION PLANS AND RESTRICTED STOCK        
Vesting period 5 years