Annual report pursuant to Section 13 and 15(d)

CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS (Details)

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CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS (Details)
$ in Thousands
 12 Months Ended
Dec. 31, 2016
USD ($)
item
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Cash, cash equivalent and short term investments        
Cash and cash equivalents $ 17,632 $ 43,456 $ 15,203 $ 20,854
Short-term Investments 57,134 82,820    
Cash, cash equivalents and short-term investments 74,766 126,276    
Available-For-Sale Securities Reconciliation        
Amortized Cost 65,048 97,911    
Gross Unrealized Gains 5 12    
Gross Unrealized Losses (23) (56)    
Fair Value $ 65,030 97,867    
Weighted-average time to maturity of cash equivalents and available-for-sale securities 91 days      
Number of investments in continuous unrealized loss position for more than twelve months | item 0      
Fair value and gross unrealized losses of investments in individual securities in unrealized loss position        
Number of individual securities in unrealized loss position for twelve months or less | item 27      
Fair Value $ 27,111      
Unrealized Losses (23)      
Money market funds        
Cash, cash equivalent and short term investments        
Cash, cash equivalents and short-term investments 9,496 26,291    
U.S. treasury bills        
Cash, cash equivalent and short term investments        
Cash, cash equivalents and short-term investments 4,300 9,048    
Available-For-Sale Securities Reconciliation        
Amortized Cost 4,300 9,061    
Gross Unrealized Losses   (13)    
Fair Value 4,300 9,048    
Government-sponsored enterprises securities        
Cash, cash equivalent and short term investments        
Cash, cash equivalents and short-term investments 16,459 48,613    
Available-For-Sale Securities Reconciliation        
Amortized Cost 16,457 48,643    
Gross Unrealized Gains 3 1    
Gross Unrealized Losses (1) (31)    
Fair Value 16,459 48,613    
Fair value and gross unrealized losses of investments in individual securities in unrealized loss position        
Fair Value 2,727      
Unrealized Losses (1)      
Corporate bonds and commercial paper        
Cash, cash equivalent and short term investments        
Cash, cash equivalents and short-term investments 44,271 40,206    
Available-For-Sale Securities Reconciliation        
Amortized Cost 44,291 40,207    
Gross Unrealized Gains 2 11    
Gross Unrealized Losses (22) (12)    
Fair Value 44,271 40,206    
Fair value and gross unrealized losses of investments in individual securities in unrealized loss position        
Fair Value 24,384      
Unrealized Losses (22)      
Cash        
Cash, cash equivalent and short term investments        
Cash, cash equivalents and short-term investments $ 240 $ 2,118