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Stock-Based Incentive Compensation Plans (Tables)
12 Months Ended
Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Schedule of Stock Option Activity
The following table summarizes stock option activity for the year ended December 31, 2018 for all stock plans:
 
Options Outstanding
 
Number of Shares
 
Weighted-Average Exercise Price
 
Weighted-Average Contractual Remaining Life
 
Aggregate Intrinsic Value
 
 
 
 
 
(Years)
 
(in thousands)
Balances at December 31, 2017
3,001,929

 
$
4.15

 
 
 
$
3,585

Options granted
100,080

 
$
8.88

 
 
 
 
Options exercised
(395,117
)
 
$
4.08

 
 
 
 
Options canceled
(65,694
)
 
$
4.81

 
 
 
 
Balances at December 31, 2018
2,641,198

 
$
4.27

 
6.6
 
$
43,905

 
 
 
 
 
 
 
 
Options vested and exercisable - December 31, 2018
1,762,687

 
$
3.73

 
5.9
 
$
41,882

 
 
 
 
 
 
 
 
Options vested and expected to vest - December 31, 2018
2,366,723

 
$
4.14

 
6.5
 
$
40,154

Schedule of Stock-Based Compensation
The following table sets forth stock-based compensation expense recognized for the periods presented (in thousands):
 
 
 
Year ended
December 31,
 
 
 
2018
 
2017
Cost of goods sold
 
 
$
34

 
$
23

Research and development
 
 
156

 
143

Sales and marketing
 
 
651

 
438

General and administrative
 
 
1,471

 
1,271

 
 
 
$
2,312

 
$
1,875

Schedule of Valuation Assumptions Related to Stock Option Awards
The grant date fair value of the stock option awards granted to employees was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions:
 
Year ended
 
December 31,
 
2018
 
2017
Expected term
6.17
 
5.71
Expected volatility
42%-47%
 
42%-55%
Risk-free interest rate
2.35%-2.96%
 
1.73%-2.31%
Dividend yield
—%
 
—%
The assumptions used to determine the grant date fair value of employee stock options and ESPP purchase rights for the periods presented are as follows:
 
Year ended
 
December 31,
 
2018
 
Expected term
0.5
 
Expected volatility
43.96%
 
Risk-free interest rate
2.49%
 
Dividend yield
—%
 
Schedule of Restricted Stock Unit Activity
The following table summarizes restricted stock units activity for the year ended December 31, 2018:
 
 
Number of
Shares
 
Weighted-
Average
Grant Date Fair
Value
Unvested as of December 31, 2017
 

 
$

Granted
 
54,036

 
$
11.79

Forfeited
 
(600
)
 
20.60

Vested
 

 
$

Unvested as of December 31, 2018
 
53,436

 
$
11.69