Equity Incentive Plans and Stock Based Compensation (Tables)
|
12 Months Ended |
Dec. 31, 2020 |
|---|
| Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] |
|
| Summary of Stock Option Activity Under Equity Incentive Plan |
The following table summarizes information about stock option activity for years ended December 31, 2020 and 2019:
|
|
|
Outstanding Options
Number of Shares
|
|
|
Weighted Average
Exercise Price
|
|
|
Weighted Average
Remaining
Contractual Term
|
|
|
Aggregate Intrinsic
Value (in millions):
|
|
|
Balances, December 31, 2018
|
|
|
4,002,999
|
|
|
$
|
10.43
|
|
|
|
6.40
|
|
|
$
|
1.50
|
|
|
Granted
|
|
|
2,023,600
|
|
|
$
|
6.00
|
|
|
|
|
|
|
|
|
|
|
Exercised
|
|
|
(286,479
|
)
|
|
$
|
6.10
|
|
|
|
|
|
|
|
|
|
|
Cancelled
|
|
|
(977,058
|
)
|
|
$
|
22.39
|
|
|
|
|
|
|
|
|
|
|
Balances, December 31, 2019
|
|
|
4,763,062
|
|
|
$
|
6.36
|
|
|
|
8.10
|
|
|
$
|
36.63
|
|
|
Granted
|
|
|
2,453,506
|
|
|
$
|
14.06
|
|
|
|
|
|
|
|
|
|
|
Exercised
|
|
|
(261,260
|
)
|
|
$
|
3.99
|
|
|
|
|
|
|
|
|
|
|
Cancelled
|
|
|
(257,381
|
)
|
|
$
|
9.99
|
|
|
|
|
|
|
|
|
|
|
Balances, December 31, 2020
|
|
|
6,697,927
|
|
|
$
|
9.13
|
|
|
|
7.76
|
|
|
$
|
13.79
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Vested and expected to vest, December 31, 2020
|
|
|
6,697,927
|
|
|
$
|
9.13
|
|
|
|
7.76
|
|
|
$
|
13.79
|
|
|
Exercisable at December 31, 2020
|
|
|
2,845,501
|
|
|
$
|
6.66
|
|
|
|
6.68
|
|
|
$
|
8.85
|
|
|
| Stock Options Outstanding and Exercisable by Exercise Price |
At December 31, 2020, stock options outstanding and exercisable by exercise price were as follows:
|
|
|
|
Options Outstanding
|
|
|
Options Exercisable
|
|
|
Range of
Exercise
Prices
|
|
Number
Outstanding
|
|
|
Weighted
Average
Remaining
Contractual
Life (Years)
|
|
|
Weighted
Average
Exercise
Price
|
|
|
Number
Exercisable
|
|
|
Weighted
Average
Exercise
Price
|
|
|
$
|
0.71-4.28
|
|
|
402,543
|
|
|
|
3.32
|
|
|
$
|
1.22
|
|
|
|
399,639
|
|
|
$
|
1.20
|
|
|
$
|
4.66-4.66
|
|
|
920,356
|
|
|
|
7.79
|
|
|
$
|
4.66
|
|
|
|
408,708
|
|
|
$
|
4.66
|
|
|
$
|
4.74-5.81
|
|
|
335,019
|
|
|
|
7.84
|
|
|
$
|
5.07
|
|
|
|
158,293
|
|
|
$
|
5.10
|
|
|
$
|
6.31-6.31
|
|
|
1,189,849
|
|
|
|
7.25
|
|
|
$
|
6.31
|
|
|
|
790,675
|
|
|
$
|
6.31
|
|
|
$
|
6.54-8.95
|
|
|
698,912
|
|
|
|
8.04
|
|
|
$
|
7.91
|
|
|
|
359,276
|
|
|
$
|
7.91
|
|
|
$
|
9.28-10.78
|
|
|
733,969
|
|
|
|
6.67
|
|
|
$
|
9.74
|
|
|
|
598,957
|
|
|
$
|
9.71
|
|
|
$
|
10.92-13.99
|
|
|
676,300
|
|
|
|
9.14
|
|
|
$
|
12.64
|
|
|
|
46,076
|
|
|
$
|
13.16
|
|
|
$
|
14.50-14.50
|
|
|
1,322,971
|
|
|
|
8.87
|
|
|
$
|
14.50
|
|
|
|
75,469
|
|
|
$
|
14.50
|
|
|
$
|
14.94-61.27
|
|
|
416,190
|
|
|
|
9.12
|
|
|
$
|
15.94
|
|
|
|
6,590
|
|
|
$
|
42.74
|
|
|
$
|
70.29-70.29
|
|
|
1,818
|
|
|
|
1.37
|
|
|
$
|
70.29
|
|
|
|
1,818
|
|
|
$
|
70.29
|
|
|
$
|
0.71-70.29
|
|
|
6,697,927
|
|
|
|
7.76
|
|
|
$
|
9.13
|
|
|
|
2,845,501
|
|
|
$
|
6.66
|
|
|
| Stock-Based Compensation Expense |
Stock-based compensation expense, which consists of the compensation cost for employee stock options and the value of options issued to non-employees for services rendered, was allocated to research and development and general and administrative in the consolidated statements of operations as follows (in thousands):
|
|
|
Year Ended
December 31,
|
|
|
|
|
2020
|
|
|
2019
|
|
|
Research and development
|
|
$
|
6,387
|
|
|
$
|
2,398
|
|
|
General and administrative
|
|
|
5,430
|
|
|
|
3,461
|
|
|
Total stock-based compensation
|
|
$
|
11,817
|
|
|
$
|
5,859
|
|
|
| Weighted-Average Fair Value Valuation Assumptions |
The fair value of employee stock options was estimated using the following weighted-average assumptions:
|
|
|
Year Ended
December 31,
|
|
|
|
|
2020
|
|
|
2019
|
|
|
Employee Stock Options:
|
|
|
|
|
|
|
|
|
|
Risk-free interest rate
|
|
|
1.44
|
%
|
|
|
2.37
|
%
|
|
Expected term (in years)
|
|
|
6.08
|
|
|
|
6.08
|
|
|
Dividend yield
|
|
|
—
|
|
|
|
—
|
|
|
Volatility
|
|
|
110.90
|
%
|
|
|
108.70
|
%
|
|
Weighted-average fair value of stock options granted
|
|
$
|
11.75
|
|
|
$
|
5.00
|
|
|