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Stock Plans and Stock-Based Compensation (Tables)
 9 Months Ended
Sep. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]  
Schedule of Assumptions Used in Determining Fair Value of Stock Option Grants

The fair value of stock option grants is determined using the Black-Scholes option pricing model with the following weighted average assumptions. In addition, the fair value per share on grant date is presented below: 

 

 

 

Three Months Ended September 30,

 

 

Nine Months Ended September 30,

 

 

 

2017

 

 

2016

 

 

2017

 

 

2016

 

Employee Stock Options:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fair value per share on grant date

 

$23.17 - $23.60

 

 

$8.94 - $9.02

 

 

$18.05 - $24.87

 

 

$8.51 - $9.02

 

Expected term (in years)

 

 

6.00

 

 

5.99 - 6.11

 

 

6.00 - 6.11

 

 

5.29 - 6.11

 

Expected volatility

 

60%

 

 

70%

 

 

60%

 

 

70%

 

Risk-free interest rate

 

1.82% - 1.93%

 

 

1.21% - 1.25%

 

 

1.82% - 2.47%

 

 

1.21% - 1.86%

 

Dividend rate

 

 

0%

 

 

 

0%

 

 

 

0%

 

 

 

0%

 

Employee Stock Purchase Plan:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Expected term (in years)

 

 

0.50

 

 

 

—

 

 

 

0.50

 

 

 

—

 

Expected volatility

 

60%

 

 

 

—

 

 

60%

 

 

 

—

 

Risk-free interest rate

 

1.18%

 

 

 

—

 

 

0.45% - 1.18%

 

 

 

—

 

Dividend rate

 

 

0%

 

 

 

—

 

 

 

0%

 

 

 

—

 

 

(1)

The expected term represents the period that the stock-based compensation awards are expected to be outstanding. Since the Company did not have sufficient historical information to develop reasonable expectations about future exercise behavior, the Company used the simplified method to compute expected term, which reflects the average of the time-to-vesting and the contractual life;

(2)

The expected volatility of the Company’s common stock on the date of grant is based on the volatilities of publicly traded peer companies that are reasonably comparable to the Company’s own operations;

(3)

The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant for zero coupon U.S. Treasury notes with maturities approximately equal to the expected term of the options; and

(4)

The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on the Company’s common stock.
Schedule of Stock Option Activity

A summary of activities under the 2008 Plan and the 2016 Plan is shown as follows for the year ended December 31, 2016 and the nine months ended September 30, 2017:

 

 

 

Stock options

outstanding

 

 

Weighted

average

exercise price

 

Outstanding at December 31, 2015

 

 

1,821,722

 

 

$

8.68

 

Granted

 

 

292,204

 

 

 

14.75

 

Exercised

 

 

(163,968

)

 

 

4.30

 

Forfeited

 

 

(65,533

)

 

 

8.03

 

Outstanding at December 31, 2016

 

 

1,884,425

 

 

 

10.02

 

Granted

 

 

997,244

 

 

 

22.47

 

Exercised

 

 

(370,084

)

 

 

5.64

 

Forfeited

 

 

(42,032

)

 

 

15.50

 

Outstanding at September 30, 2017

 

 

2,469,553

 

 

$

15.61

 

 
Schedule of Stock Options Outstanding and Options Exercisable and Vested

Stock options outstanding, and options exercisable and vested are as follows:

 

Outstanding as of

September 30, 2017

 

 

Remaining

contractual

life (years)

 

 

Weighted

average

exercise price

 

 

Exercisable

as of

September 30,

2017

 

 

Remaining

contractual

life (years)

 

 

Weighted

average

exercise price

 

 

2,469,553

 

 

 

8.36

 

 

$

15.61

 

 

 

768,956

 

 

 

7.03

 

 

$

9.45

 

 

Outstanding as of

December 31, 2016

 

 

Remaining

contractual

life (years)

 

 

Weighted

average

exercise price

 

 

Exercisable

as of

December 31,

2016

 

 

Remaining

contractual

life (years)

 

 

Weighted

average

exercise price

 

 

1,884,425

 

 

 

7.86

 

 

$

10.02

 

 

 

809,900

 

 

 

7.13

 

 

$

6.81

 

 
Schedule of Vested and Nonvested Stock Option Activity

Vested and nonvested stock option activity was as follows:

 

 

 

Vested

 

 

Nonvested

 

 

 

Options

outstanding

 

 

Weighted

average

exercise

price

 

 

Options

outstanding

 

 

Weighted

average

exercise

price

 

Outstanding at September 30, 2017

 

 

768,956

 

 

$

9.45

 

 

 

1,700,597

 

 

$

18.40

 

Outstanding at December 31, 2016

 

 

809,900

 

 

$

6.81

 

 

 

1,074,525

 

 

$

12.44

 

 
Schedule of Stock-Based Compensation Expense

The Company recorded the total stock-based compensation expense as follows (in thousands):

 

 

 

Three Months Ended September 30,

 

 

Nine Months Ended September 30,

 

 

 

2017

 

 

2016

 

 

2017

 

 

2016

 

Cost of revenue

 

$

141

 

 

$

46

 

 

$

266

 

 

$

135

 

Sales and marketing

 

 

691

 

 

 

211

 

 

 

1,250

 

 

 

503

 

Research and development

 

 

416

 

 

 

87

 

 

 

738

 

 

 

263

 

General and administrative

 

 

1,555

 

 

 

415

 

 

 

2,618

 

 

 

1,264

 

Total

 

$

2,803

 

 

$

759

 

 

$

4,872

 

 

$

2,165