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SHAREHOLDERS' EQUITY - Deferred Compensation Arrangement - Additional Information (Details) - USD ($)
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Deferred Compensation Arrangement with Employees and Non-Employees, Share-Based Payments [Line Items]    
Fair value of shares withheld for tax withholding obligations $ 5,832,000  
Employees and Non Employee Members of Scientific Advisory Board [Member]    
Deferred Compensation Arrangement with Employees and Non-Employees, Share-Based Payments [Line Items]    
Shares issued (in shares) 2,456 5,590
Employees [Member]    
Deferred Compensation Arrangement with Employees and Non-Employees, Share-Based Payments [Line Items]    
Fair value of shares issued $ 0 $ 165,000
Shares withheld for tax withholding obligations (in shares)   605
Fair value of shares withheld for tax withholding obligations   $ 55,000
Members of Scientific Advisory Board [Member]    
Deferred Compensation Arrangement with Employees and Non-Employees, Share-Based Payments [Line Items]    
Fair value of shares issued $ 300,000 $ 300,000