EQUITY AWARDS (Tables)
 12 Months Ended
Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Summary of Stock Option Plan Activity
A summary of stock option plan activity (including the performance-based options) for the years ended December 31, 2014, 2013, and 2012 is provided below:
 
Options
Outstanding
 
Weighted
Average
Exercise
Price
 
Weighted
Average
Grant Date
Fair Value
 
Weighted
Average
Remaining
Contractual
Life (in years)
 
Aggregate
Intrinsic
Value
(in thousands)
December 31, 2011
1,781,499

 
$
3.90

 
$
2.59

 
 
 
 
Options granted
2,193,701

 
1.46

 
1.07

 
 
 
 
Forfeited
(90,007
)
 
3.48

 
2.52

 
 
 
 
December 31, 2012
3,885,193

 
2.53

 
1.73

 
 
 
 
Options granted
564,442

 
1.29

 
0.93

 
 
 
 
Forfeited
(15,929
)
 
1.53

 
1.09

 
 
 
 
December 31, 2013
4,433,706

 
2.38

 
1.63

 
 
 
 
Options granted
2,072,108

 
2.98

 
2.34

 
 
 
 
Exercised
(41,828
)

2.51


1.73

 
 
 
 
December 31, 2014
6,463,986

 
$
2.57

 
$
1.86

 
4.6
 
 
Options exercisable on December 31, 2014
3,297,814

 
$
2.70

 
 

 
3.3
 
$
3,571

Options expected to vest as of December 31, 2014
3,166,172

 
2.43

 
 

 
 
 
3,158


On December 31, 2014, options outstanding had exercise prices ranging from $0.71 to $5.93 and options exercisable had exercise prices ranging from $0.71 to $5.93.
Assumptions Used to Estimate Fair Value of Stock Options Granted
We used the Black-Scholes option pricing model to estimate the fair value of stock options granted in 2014, 2013, and 2012, with the following assumptions:
 
2014
 
2013
 
2012
Expected weighted-average life of options granted
4.5 years
 
4.5 years
 
3.0 - 5.0 years
Range of volatility rates based on historical industry volatility
115.45% - 116.47%
 
100.52%
 
94.39% - 102.22%
Range of risk-free interest rates
1.66% - 1.74%
 
0.81%
 
.57% - .83%
Expected dividend yield
—
 
—
 
—