Equity Incentive Plans, Employee Stock Purchase Plan and Stock-Based Compensation (Tables)
|
6 Months Ended |
Jun. 30, 2021 |
|---|
| Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] |
|
| Summary of Option Activity |
The following table summarizes option activity under the Company’s 2004 Plan and 2018 Plan:
|
|
|
Shares
|
|
|
Weighted-
Average
Exercise Price
|
|
|
Weighted-
Average
Remaining
Contract Term
(Years)
|
|
|
Aggregate
Intrinsic Value
(in thousands)
|
|
|
Stock options outstanding at December 31, 2020
|
|
|
5,439,295
|
|
|
$
|
11.93
|
|
|
|
7.75
|
|
|
$
|
53,202
|
|
|
Granted
|
|
|
1,046,950
|
|
|
$
|
20.85
|
|
|
|
|
|
|
|
|
|
|
Exercised
|
|
|
(170,063
|
)
|
|
$
|
10.65
|
|
|
|
|
|
|
|
|
|
|
Canceled and forfeited
|
|
|
(65,251
|
)
|
|
$
|
10.77
|
|
|
|
|
|
|
|
|
|
|
Stock options outstanding at June 30, 2021
|
|
|
6,250,931
|
|
|
$
|
13.47
|
|
|
|
7.80
|
|
|
$
|
34,469
|
|
|
Stock options exercisable at June 30, 2021
|
|
|
3,166,329
|
|
|
$
|
12.57
|
|
|
|
6.94
|
|
|
$
|
19,218
|
|
|
| Schedule of Employee Stock Options Valuation |
For determining stock-based compensation expense, the fair-value-based measurement of each employee stock option was estimated as of the date of grant using the Black-Scholes option-pricing model with assumptions as follows:
|
|
|
Six Months Ended
|
|
|
|
|
June 30,
|
|
|
|
|
2021
|
|
|
2020
|
|
|
Expected term (in years)
|
|
5.3-6.1
|
|
|
2.8-7.0
|
|
|
Expected volatility
|
|
84.6%-84.9%
|
|
|
73.2%-84.0%
|
|
|
Risk-free interest rate
|
|
0.6%-1.1%
|
|
|
0.2%-1.6%
|
|
|
Expected dividend
|
|
|
–
|
|
|
|
–
|
|
|
| Summary of Status and Activity of Non-vested RSUs |
A summary of the status and activity of non-vested RSUs during the six months ended June 30, 2021 is as follows:
|
|
|
Number of
shares
|
|
|
Weighted
Average
Grant-Date
Fair Value
|
|
|
Non-vested December 31, 2020
|
|
|
666,375
|
|
|
$
|
9.83
|
|
|
Granted
|
|
|
1,511,750
|
|
|
$
|
21.02
|
|
|
Vested and released
|
|
|
(151,099
|
)
|
|
$
|
9.03
|
|
|
Canceled and forfeited
|
|
|
(38,600
|
)
|
|
$
|
16.46
|
|
|
Non-vested June 30, 2021
|
|
|
1,988,426
|
|
|
$
|
18.27
|
|
|
| Schedule of Fair Value of ESPP Shares Using Option Pricing Model |
For the six months ended June 30, 2021 and 2020, the fair value of ESPP shares was estimated using the following assumptions:
|
|
Six Months Ended
|
|
|
|
June 30,
|
|
|
|
2021
|
|
|
2020
|
|
|
Expected term (in years)
|
0.5
|
|
|
0.5
|
|
|
Expected volatility
|
72.5-111.4
|
%
|
|
|
63.0
|
%
|
|
Risk-free interest rate
|
|
0.1
|
%
|
|
|
1.9
|
%
|
|
Expected dividend
|
|
–
|
|
|
|
–
|
|
|
| Schedule of Stock-Based Compensation Expense Recognized |
Total stock-based compensation expense recognized was as follows:
|
|
|
Three Months Ended
|
|
|
Six Months Ended
|
|
|
|
|
June 30,
|
|
|
June 30,
|
|
|
|
|
2021
|
|
|
2020
|
|
|
2021
|
|
|
2020
|
|
|
|
|
(in thousands)
|
|
|
(in thousands)
|
|
|
Research and development expense:
|
|
$
|
1,845
|
|
|
$
|
696
|
|
|
$
|
2,949
|
|
|
$
|
1,211
|
|
|
General and administrative expense:
|
|
$
|
4,062
|
|
|
|
2,315
|
|
|
|
6,910
|
|
|
|
4,507
|
|
|
Total
|
|
$
|
5,907
|
|
|
$
|
3,011
|
|
|
$
|
9,859
|
|
|
$
|
5,718
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| Summary of the Status of Call Options |
A summary of the status of the call options as of June 30, 2021 and December 31, 2020 is as follows:
|
|
|
June 30,
|
|
|
December 31,
|
|
|
|
|
2021
|
|
|
2020
|
|
|
|
|
Shares
|
|
|
Shares
|
|
|
Options vested and exercised
|
|
|
257,834
|
|
|
|
257,834
|
|
|
Options vested and outstanding
|
|
|
4,445
|
|
|
|
-
|
|
|
Options unvested and outstanding
|
|
|
4,445
|
|
|
|
8,890
|
|
|
Total options granted
|
|
|
266,724
|
|
|
|
266,724
|
|
|