Equity Incentive Plans, Employee Stock Purchase Plan and Stock-Based Compensation (Tables)
|
3 Months Ended |
Mar. 31, 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
|
|
|
853,950
|
|
|
$
|
21.35
|
|
|
|
|
|
|
|
|
|
Exercised
|
|
|
(129,161
|
)
|
|
$
|
10.53
|
|
|
|
|
|
|
|
|
|
Canceled and forfeited
|
|
|
(45,708
|
)
|
|
$
|
11.20
|
|
|
|
|
|
|
|
|
|
Stock options outstanding at March 31, 2021
|
|
|
6,118,376
|
|
|
$
|
13.28
|
|
|
|
7.98
|
|
|
$
|
58,149
|
|
Stock options exercisable at March 31, 2021
|
|
|
2,779,423
|
|
|
$
|
12.53
|
|
|
|
6.97
|
|
|
$
|
28,424
|
|
|
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:
|
|
Three Months Ended
|
|
|
|
March 31,
|
|
|
|
2021
|
|
|
2020
|
|
Expected term (in years)
|
|
5.8-6.1
|
|
|
5.1-7.0
|
|
Expected volatility
|
|
84.6-84.9%
|
|
|
73.2%-77.3%
|
|
Risk-free interest rate
|
|
0.6-1.0%
|
|
|
0.8%-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 three months ended March 31, 2021 is as follows:
|
|
Number of
shares
|
|
|
Weighted
Average
Grant-Date
Fair Value
|
|
Non-vested December 31, 2020
|
|
|
666,375
|
|
|
$
|
9.83
|
|
Granted
|
|
|
1,435,750
|
|
|
$
|
21.11
|
|
Vested and released
|
|
|
(147,349
|
)
|
|
$
|
9.02
|
|
Canceled and forfeited
|
|
|
(20,275
|
)
|
|
$
|
14.13
|
|
Non-vested March 31, 2021
|
|
|
1,934,501
|
|
|
$
|
18.22
|
|
|
Schedule of Fair Value of ESPP Shares Using Option Pricing Model |
For the three months ended March 31, 2021 and 2020, the fair value of ESPP shares was estimated using the following assumptions:
|
Three Months Ended
|
|
|
March 31,
|
|
|
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
|
|
|
|
March 31,
|
|
|
|
2021
|
|
|
2020
|
|
|
|
(in thousands)
|
|
Research and development expense:
|
|
$
|
1,104
|
|
|
$
|
515
|
|
General and administrative expense:
|
|
|
2,848
|
|
|
|
2,192
|
|
Total
|
|
$
|
3,952
|
|
|
$
|
2,707
|
|
|
|
|
|
|
|
|
|
|
|
Summary of the Status of Call Options |
A summary of the status of the call options as of March 31, 2021 and December 31, 2020 is as follows:
|
|
March 31,
|
|
|
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
|
|
|