Annual report pursuant to Section 13 and 15(d)

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

v3.8.0.1
STOCK-BASED COMPENSATION - Employee Stock Purchase Plan (Details)
 12 Months Ended
Dec. 31, 2017
$ / shares
item
shares
Dec. 31, 2016
$ / shares
shares
Dec. 31, 2015
$ / shares
shares
Jul. 01, 2016
USD ($)
Jan. 02, 2015
USD ($)
Stock Based Compensation          
Total incremental fair value for the Purchase Plan reset | $       $ 1,000,000 $ 792,000
Purchase plan          
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 403,302 482,746 576,537    
Average price of shares issued (in dollars per share) | $ / shares 1.87 1.89 2.03    
Weighted average fair value of stock purchased (in dollars per share) | $ / shares $ 0.99 $ 0.98 $ 1.05    
Number of shares of common stock available for future issuance | shares 2,115,568        
Award offering period 24 months        
Number of purchase periods per award offering period | item 4        
Award purchase period 6 months