Annual report pursuant to Section 13 and 15(d)

STOCK-BASED COMPENSATION - Employee Stock Purchase Plan (Details)

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STOCK-BASED COMPENSATION - Employee Stock Purchase Plan (Details) - Purchase Plan
12 Months Ended
Dec. 31, 2019
USD ($)
$ / shares
shares
Dec. 31, 2018
$ / shares
shares
Dec. 31, 2017
$ / shares
shares
Stock Based Compensation      
Purchase price expressed as a percentage of fair market value of common stock on the first day of the offering period 85.00%    
Purchase price expressed as a percentage of fair market value of common stock on the purchase date 85.00%    
Number of shares of common stock issued | shares 747,691 783,984 403,302
Average price of shares issued (in dollars per share) | $ / shares 1.92 1.92 1.87
Weighted average fair value of stock purchased (in dollars per share) | $ / shares $ 1.07 $ 1.27 $ 0.99
Number of shares of common stock available for future issuance | shares 583,893    
Award offering period 24 months    
Total incremental fair value for the Purchase Plan reset | $ $ 753,000