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Stock Plans and Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 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 assumptions.

 

 

Year Ended December 31,

 

 

 

2017

 

 

2016

 

 

2015

 

Employee Stock Options:

 

 

 

 

 

 

 

 

 

 

 

 

Fair value of common stock

 

$18.05 - $26.50

 

 

$14.21 - $18.83

 

 

$9.37 - $13.63

 

Expected term (in years)

 

6.00 - 6.11

 

 

5.29 - 6.11

 

 

5.09 - 6.15

 

Expected volatility

 

50% - 60%

 

 

60% - 70%

 

 

60%

 

Risk-free interest rate

 

1.82% - 2.47%

 

 

1.21% - 2.55%

 

 

1.41% - 1.94%

 

Dividend rate

 

0%

 

 

0%

 

 

0%

 

Employee Stock Purchase Plan:

 

 

 

 

 

 

 

 

 

 

 

 

Expected term (in years)

 

 

0.50

 

 

 

0.50

 

 

 

—

 

Expected volatility

 

60%

 

 

60%

 

 

 

—

 

Risk-free interest rate

 

0.45% - 1.18%

 

 

0.45%

 

 

 

—

 

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 have 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 2016 Plan is shown as follows for the years ended December 31, 2017 and 2016:

 

 

 

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

 

 

1,096,881

 

 

$

22.84

 

Exercised

 

 

(497,175

)

 

$

5.77

 

Forfeited

 

 

(43,841

)

 

$

15.60

 

Outstanding at December 31, 2017

 

 

2,440,290

 

 

$

16.55

 

 
Schedule of Stock Options Outstanding and Options Exercisable and Vested

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

 

Outstanding as of

December 31, 2017

 

 

Remaining

contractual

life (years)

 

 

Weighted

average

exercise

price

 

 

Exercisable

as of

December 31,

2017

 

 

Remaining

contractual

life (years)

 

 

Weighted

average

exercise

price

 

 

2,440,290

 

 

 

8.28

 

 

$

16.55

 

 

 

748,148

 

 

 

7.00

 

 

$

10.39

 

 

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 under the 2008 Plan and 2016 Plan was as follows:

 

 

 

Vested

 

 

Nonvested

 

 

 

Options

outstanding

 

 

Weighted

average

exercise

price

 

 

Options

outstanding

 

 

Weighted

average

exercise

price

 

Outstanding at December 31, 2017

 

 

748,148

 

 

$

10.39

 

 

 

1,692,142

 

 

$

19.27

 

Outstanding at December 31, 2016

 

 

809,900

 

 

$

6.81

 

 

 

1,074,525

 

 

$

12.44

 

 
Schedule of Restricted Stock Unit Activity and Market-based Restricted Stock Unit Activity

A summary of activity in connection with our RSUs and market-based RSUs for the year ended December 31, 2017 is as follows:

 

 

 

Number of Shares

 

Outstanding as of December 31, 2016

 

 

—

 

Granted

 

 

784,000

 

Vested

 

 

—

 

Forfeited

 

 

—

 

Outstanding as of December 31, 2017

 

 

784,000

 

 
Schedule of Classification of Stock-Based Compensation Relating to Stock Options and RSUs

The Company classified stock based compensation relating to stock options and RSUs in the following captions in the accompanying consolidated statements of operations and comprehensive loss:

 

 

 

Year Ended December 31,

 

 

 

2017

 

 

2016

 

 

2015

 

 

 

(in thousands)

 

Cost of revenue

 

$

578

 

 

$

180

 

 

$

150

 

Sales and marketing

 

 

2,419

 

 

 

725

 

 

 

315

 

Research and development

 

 

1,514

 

 

 

348

 

 

 

297

 

General and administrative

 

 

4,788

 

 

 

1,848

 

 

 

760

 

Total

 

$

9,299

 

 

$

3,101

 

 

$

1,522