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DERIVATIVE INSTRUMENTS (Tables)
 12 Months Ended
Dec. 31, 2017
DERIVATIVE INSTRUMENTS  
Assumptions used in determining fair value of warrants

 

 

 

 

 

 

 

 

 

 

December 31, 

 

 

    

2017

    

2016

    

2015

 

Risk-free interest rate

 

1.91

% 

1.20

% 

0.65

% 

Expected dividend yield

 
0

% 
0

% 
0

% 

Contractual term

 
1.35

years
2.4

years
3.4

years

Expected volatility

 

82

% 

89

% 

100

% 

 

Changes in derivative warrant liability

 

 

 

 

 

 

 

 

 

 

 

 

 

Year Ended December 31, 

 

 

    

2017

    

2016

    

2015

 

Balance at beginning of year

 

$

1,314

 

$

1,907

 

$

7,224

 

Increase in derivative liability prior to warrant exchange

 

 

3,029

 

 

 —

 

 

 —

 

Reduction in derivative liability due to warrant exchange

 

 

(3,537)

 

 

 —

 

 

 —

 

Repurchase of warrants

 

 

(40)

 

 

 —

 

 

 —

 

Fair value of derivative warrant liability reclassified to additional paid in capital

 

 

 —

 

 

 —

 

 

(16,121)

 

Increase (decrease) in the fair value of warrants

 

 

(762)

 

 

(593)

 

 

10,804

 

Balance at end of year

 

$

 4

 

$

1,314

 

$

1,907