Equity Incentive Plans, Employee Stock Purchase Plan and Stock-Based Compensation (Tables)
|
12 Months Ended |
Dec. 31, 2021 |
|---|
| Share-based Payment Arrangement [Abstract] |
|
| Summary of Option Activity |
The following table summarizes option activities under the Company’s 2004 Plan, 2018 Plan and 2021 Plan:
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Outstanding
Options |
|
|
Weighted-
Average
Exercise Price |
|
|
Weighted-
Average
Remaining
Contract Term
(Years) |
|
|
Aggregate
Intrinsic Value
(in thousands) |
|
Balances at December 31, 2020 |
|
|
5,439,295 |
|
|
$ |
11.93 |
|
|
|
7.75 |
|
|
$ |
53,202 |
|
Granted |
|
|
1,449,834 |
|
|
$ |
20.27 |
|
|
|
|
|
|
|
Exercised |
|
|
(237,370 |
) |
|
$ |
10.47 |
|
|
|
|
|
|
|
Canceled/Forfeited |
|
|
(139,673 |
) |
|
$ |
10.94 |
|
|
|
|
|
|
|
Balances at December 31, 2021 |
|
|
6,512,086 |
|
|
$ |
13.86 |
|
|
|
7.39 |
|
|
$ |
14,955 |
|
Exercisable at December 31, 2021 |
|
|
3,866,289 |
|
|
$ |
12.91 |
|
|
|
6.63 |
|
|
$ |
9,170 |
|
|
| 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:
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Year Ended December 31, |
|
|
|
2021 |
|
|
2020 |
|
|
2019 |
|
Expected term (in years) |
|
5.3-6.1 |
|
|
3.1-7.0 |
|
|
4.5-7.0 |
|
Expected volatility |
|
80.9%-84.9% |
|
|
73.2%-87.4% |
|
|
72.7%-74.9% |
|
Risk-free interest rate |
|
0.6%-1.3% |
|
|
0.2%-1.6% |
|
|
1.4%-2.6% |
|
Expected dividend |
|
|
- |
|
|
|
- |
|
|
|
- |
|
|
| Summary of Status and Activity of Non-vested RSUs |
A summary of the status and activity of non-vested RSUs for the year ended December 31, 2021 is as follows:
|
|
|
|
|
|
|
|
|
|
|
Number of
Shares |
|
|
Weighted
Average
Grant-Date
Fair Value |
|
Non-vested December 31, 2020 |
|
|
666,375 |
|
|
$ |
9.83 |
|
Granted |
|
|
2,094,250 |
|
|
|
20.31 |
|
Released |
|
|
(238,724 |
) |
|
|
11.23 |
|
Canceled |
|
|
(118,075 |
) |
|
|
17.66 |
|
Non-vested December 31, 2021 |
|
|
2,403,826 |
|
|
$ |
18.43 |
|
|
| Schedule of Fair Value of ESPP Shares Using Option Pricing Model |
For the years ended December 31, 2021, 2020 and 2019, the fair value of ESPP shares was estimated using the following assumptions:
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Year Ended December 31, |
|
|
|
|
|
|
2021 |
|
|
2020 |
|
|
2019 |
|
Expected term (in years) |
|
0.5 |
|
|
0.5 |
|
|
0.5 |
|
Expected volatility |
|
65.9-111.4% |
|
|
63.0%-111.4% |
|
|
63.0%-83.2% |
|
Risk-free interest rate |
|
|
0.1 |
% |
|
0.1%-1.9% |
|
|
1.9%-2.5% |
|
Expected dividend |
|
|
- |
|
|
|
- |
|
|
|
- |
|
|
| Schedule of Stock-Based Compensation Expense Recognized |
Total stock-based compensation expense recognized was as follows:
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Year Ended December 31, |
|
|
|
2021 |
|
|
2020 |
|
|
2019 |
|
|
|
(in thousands) |
|
Research and development expense: |
|
|
|
|
|
|
|
|
|
Stock options |
|
$ |
2,208 |
|
|
$ |
1,405 |
|
|
$ |
903 |
|
Restricted stock units |
|
|
4,280 |
|
|
|
770 |
|
|
|
623 |
|
ESPP |
|
|
638 |
|
|
|
512 |
|
|
|
389 |
|
Subtotal |
|
|
7,126 |
|
|
|
2,687 |
|
|
|
1,915 |
|
General and administrative expense: |
|
|
|
|
|
|
|
|
|
Stock options |
|
|
11,045 |
|
|
|
7,098 |
|
|
|
6,815 |
|
Restricted stock units |
|
|
4,920 |
|
|
|
2,021 |
|
|
|
1,464 |
|
ESPP |
|
|
150 |
|
|
|
111 |
|
|
|
118 |
|
Subtotal |
|
|
16,115 |
|
|
|
9,230 |
|
|
|
8,397 |
|
Total |
|
$ |
23,241 |
|
|
$ |
11,917 |
|
|
$ |
10,312 |
|
|
| Summary of the Status of Call Options |
A summary of the status of the call options at December 31, 2021 and 2020 is as follows:
|
|
|
|
|
|
|
|
|
|
|
|
December 31, 2021 |
|
|
December 31, 2020 |
|
|
|
|
Shares |
|
|
Shares |
|
|
Options vested and exercised |
|
|
262,279 |
|
|
|
257,834 |
|
|
Options vested and outstanding |
|
- |
|
|
- |
|
|
Options unvested and outstanding |
|
|
4,445 |
|
|
|
8,890 |
|
|
Total options granted |
|
|
266,724 |
|
|
|
266,724 |
|
|
|
|
|
|
|
|
|
|
|