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Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]  
Summary of Company's Stock Option Activity and Related Information

A summary of the Company’s stock option activity and related information is as follows:

 

 

 

 

 

 

 

Options Outstanding

 

 

 

Shares

Available

for Grant

 

 

Number

of Stock

Options

Outstanding

 

 

Weighted-

Average

Exercise

Price

 

 

Weighted-

Average

Remaining

Contractual Life

(Years)

 

 

Aggregate

Intrinsic

Value

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(In thousands)

 

Balance at December 31, 2017

 

 

969,783

 

 

 

8,592,747

 

 

$

3.69

 

 

 

7.4

 

 

$

47,864

 

Additional authorized

 

 

8,326,158

 

 

 

—

 

 

 

 

 

 

 

 

 

 

 

 

 

Granted

 

 

(6,997,114

)

 

 

6,997,114

 

 

 

8.44

 

 

 

 

 

 

 

 

 

Exercised

 

 

—

 

 

 

(2,608,812

)

 

 

2.03

 

 

 

 

 

 

 

 

 

Cancelled

 

 

1,377,341

 

 

 

(1,377,341

)

 

 

6.12

 

 

 

 

 

 

 

 

 

RSUs granted

 

 

(1,767,542

)

 

 

—

 

 

 

 

 

 

 

 

 

 

 

 

 

Balance at December 31, 2018

 

 

1,908,626

 

 

 

11,603,708

 

 

$

6.64

 

 

 

7.6

 

 

$

10,151

 

Vested and exercisable at December 31, 2018

 

 

 

 

 

 

4,299,323

 

 

$

4.28

 

 

 

5.7

 

 

$

8,581

 

Vested and expected to vest at December 31, 2018

 

 

 

 

 

 

11,124,469

 

 

$

6.58

 

 

 

7.6

 

 

$

10,092

 
Schedule of Weighted-Average Assumptions Used in Black-Scholes Option-Pricing Model to Estimate Fair Value of Employee Stock Options at Grant Date

The fair value of employee stock options was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted-average assumptions:

 

 

 

Year Ended December 31,

 

 

 

2018

 

 

2017

 

 

2016

 

Expected term (in years)

 

 

6.0

 

 

 

5.9

 

 

 

6.0

 

Expected volatility (%)

 

60.4%

 

 

66.0%

 

 

67.1%

 

Risk-free interest rate (%)

 

2.8%

 

 

2.1%

 

 

1.3%

 

Expected dividend yield (%)

 

0%

 

 

0%

 

 

0%

 
Summary of RSU Activity (Detail)

A summary of the Company’s RSU activity and related information is as follows:

 

 

RSUs

 

 

 

 

Number of Shares

 

 

Weighted Average Grant Date Fair Value

 

 

Unvested at December 31, 2017

 

 

—

 

 

$

—

 

 

RSUs granted

 

 

1,767,542

 

 

$

9.65

 

 

RSUs vested

 

 

(31,308

)

 

$

9.17

 

 

Unvested at December 31, 2018

 

 

1,736,234

 

 

$

9.65

 

 

Vested and unreleased

 

 

121,507

 

 

 

 

 

 

Outstanding at December 31 2018

 

 

1,857,741

 

 

 

 

 

 

 
Summary of Stock-Based Compensation Expense

Total stock-based compensation expense recognized in the Company’s consolidated statements of operations and comprehensive loss is classified as follows (in thousands):

 

 

 

Year Ended December 31,

 

 

 

2018

 

 

2017

 

 

2016

 

Research and development

 

$

1,411

 

 

$

952

 

 

$

593

 

Selling and marketing

 

 

700

 

 

 

303

 

 

 

120

 

General and administrative

 

 

12,058

 

 

 

4,064

 

 

 

2,194

 

Total stock-based compensation expense

 

$

14,169

 

 

$

5,319

 

 

$

2,907