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Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]  
Summary of Employee and Non-Employee Stock Option Activity

 

The following table summarizes employee and non-employee stock option activity for the year ended December 31, 2019:

 

 

 

Shares

Issuable

Under

Options

 

 

Weighted

Average

Exercise

Price

 

 

Weighted

Average

Remaining

Contractual

Term

 

 

Aggregate

Intrinsic

Value

 

 

 

 

 

 

 

 

 

 

 

(in years)

 

 

(in thousands)

 

Outstanding as of December 31, 2018

 

 

3,142,687

 

 

$

6.67

 

 

 

8.52

 

 

$

4,798

 

Granted

 

 

1,516,900

 

 

 

8.09

 

 

 

 

 

 

 

 

 

Exercised

 

 

(274,436

)

 

 

4.16

 

 

 

 

 

 

 

 

 

Forfeited

 

 

(495,963

)

 

 

6.94

 

 

 

 

 

 

 

 

 

Outstanding as of December 31, 2019

 

 

3,889,188

 

 

$

7.37

 

 

 

8.10

 

 

$

3,642

 

Options vested and expected to vest as of

   December 31, 2019

 

 

3,762,950

 

 

$

7.31

 

 

 

8.09

 

 

$

3,637

 

Options exercisable as of December 31, 2019

 

 

1,767,376

 

 

$

6.67

 

 

 

7.25

 

 

$

2,774

 
Summary of Stock-Based Compensation Expense

Total stock-based compensation expense recognized from the Company’s equity incentive plans, 2018 Plan, and the 2016 ESPP for the years ended December 31, 2019, 2018, and 2017 was as follows (in thousands):

 

 

 

Year Ended December 31,

 

 

 

2019

 

 

2018

 

 

2017

 

 

 

Employees

 

 

Non-

Employees

 

 

Employees

 

 

Non-

Employees

 

 

Employees

 

 

Non-

Employees

 

Research and development

 

$

1,828

 

 

$

—

 

 

$

1,440

 

 

$

234

 

 

$

961

 

 

$

—

 

General and administrative

 

 

3,048

 

 

 

—

 

 

 

2,606

 

 

 

—

 

 

 

1,531

 

 

 

—

 

Total stock-based

   compensation expense

 

$

4,876

 

 

$

—

 

 

$

4,046

 

 

$

234

 

 

$

2,492

 

 

$

—

 
Summary of Weighted-Average Assumptions Used in Calculating Fair Value of Awards The following table summarizes the weighted-average assumptions used in calculating the fair value of the awards:

 

 

 

Year Ended December 31,

 

 

 

2019

 

 

2018

 

 

2017

 

2018 Plan, 2016 Plan, and 2015 Plan

 

 

 

 

 

 

 

 

 

 

 

 

Expected term (in years)

 

 

6.01

 

 

 

5.20

 

 

 

5.88

 

Expected volatility

 

 

80

%

 

 

74

%

 

 

86

%

Risk-free interest

 

 

2.32

%

 

 

2.42

%

 

 

2.00

%

Dividend yield

 

 

0

%

 

 

0

%

 

 

0

%

2016 ESPP

 

 

 

 

 

 

 

 

 

 

 

 

Expected term (in years)

 

 

0.50

 

 

 

0.50

 

 

 

0.50

 

Expected volatility

 

 

70

%

 

 

66

%

 

 

78

%

Risk-free interest

 

 

2.11

%

 

 

2.20

%

 

 

1.06

%

Dividend yield

 

 

0

%

 

 

0

%

 

 

0

%