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Stock-Based Compensation (Tables)
 6 Months Ended
Jun. 30, 2014
Summary of Stock Based Compensation Expense

The following table summarizes the stock-based compensation expense recognized in the three and six months ended June 30, 2014 and 2013 (in thousands):

 

 

Three Months Ended
June  30,

 

  

Six Months Ended
June 30,

 

(in thousands)

2014

 

  

2013

 

  

2014

 

  

2013

 

Cost of goods sold

$

455

  

  

$

131

  

  

$

785

  

  

$

374

  

Research and development

 

408

  

  

 

600

  

  

 

1,115

  

  

 

1,018

  

Sales and marketing

 

587

  

  

 

344

  

  

 

960

  

  

 

582

  

General and administrative

 

273

  

  

 

398

  

  

 

764

  

  

 

701

  

 

$

1,723

  

  

$

1,473

  

  

$

3,624

  

  

$

2,675

  

 
Estimated Fair Value of Certain Stock-Based Awards Using Black-Scholes-Merton Valuation Model

The Company estimated the fair value of certain stock-based awards using a Black-Scholes-Merton valuation model with the following assumptions:

 

 

Three Months Ended June 30,

 

 

Six Months Ended June 30,

 

 

2014

 

 

2013

 

 

2014

 

 

2013

 

Stock options

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Weighted-average expected term (years)

 

5.12

 

 

6.30

 

 

 

5.12

 

 

 

6.34

 

Weighted-average volatility

 

69%

 

 

75%

 

 

 

70%

 

 

 

75%

 

Risk-free interest rate

 

1.73%

 

 

1.12 – 1.14%

 

 

 

1.73 – 1.75%

 

 

 

1.08 – 1.14%

 

Expected dividends

 

—

 

 

—

 

 

 

—

 

 

 

—

 

Stock appreciation units

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Weighted-average expected term (years)

 

2.40

 

 

2.33

 

 

 

2.27

 

 

 

2.47

 

Weighted-average volatility

 

56%

 

 

57%

 

 

 

57%

 

 

 

60%

 

Risk-free interest rate

 

0.13 - 0.90%

 

 

0.19 – 0.30%

 

 

 

0.13 – 0.90%

 

 

 

0.19 – 0.46%

 

Expected dividends

 

—

 

 

—

 

 

 

—

 

 

 

—

 

ESPP

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Weighted-average expected term (years)

 

0.40

 

 

0.73

 

 

 

0.69

 

 

 

0.73

 

Weighted-average volatility

 

56%

 

 

48%

 

 

 

54%

 

 

 

48%

 

Risk-free interest rate

 

0.05%

 

 

0.09 – 0.16%

 

 

 

0.05 – 0.13%

 

 

 

0.09 – 0.16%

 

Expected dividends

 

—

 

 

—

 

 

 

—

 

 

 

—

 

 
Summary of Stock Option and Restricted Stock Unit Activity

The following table summarizes the Company’s stock option and RSU activity during the six months ended June 30, 2014:

 

 

Stock Options

 

  

Restricted Stock Units

 

 

Number
of
shares

 

 

Weighted
average
exercise
price

 

  

Number
of
units

 

 

Weighted
average
grant date
fair value

 

Balance at December 31, 2013

 

4,103,454

  

 

$

5.92

  

  

 

1,169,649

  

 

$

6.42

  

Granted

 

51,800

 

 

 

6.08

 

 

 

26,000

 

 

 

7.62

  

Exercised/Converted

 

(173,723

)

 

 

4.25

 

 

 

(47,682

)

 

 

6.04

  

Forfeited

 

(131,458

)

 

 

5.45

 

 

 

(35,034

)

 

 

6.42

  

Balance at June 30, 2014

 

3,850,073

 

 

 

6.01

 

 

 

1,112,933

 

 

 

6.47