Equity Incentive Plans and Stock Based Compensation (Tables)
|
12 Months Ended |
Dec. 31, 2019 |
|---|
| 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, 2019 and 2018:
|
|
|
Outstanding Options
Number of Shares
|
|
|
Weighted Average
Exercise Price
|
|
|
Weighted Average
Remaining
Contractual Term
|
|
|
Aggregate Intrinsic
Value of
December 31, 2018
(in millions):
|
|
|
Balances, December 31, 2017
|
|
|
2,768,711
|
|
|
$
|
12.07
|
|
|
|
5.6
|
|
|
$
|
11.0
|
|
|
Options granted
|
|
|
1,844,787
|
|
|
|
6.98
|
|
|
|
|
|
|
|
|
|
|
Options exercised
|
|
|
(407,682
|
)
|
|
|
0.70
|
|
|
|
|
|
|
|
|
|
|
Options canceled
|
|
|
(202,817
|
)
|
|
|
20.83
|
|
|
|
|
|
|
|
|
|
|
Balances, December 31, 2018
|
|
|
4,002,999
|
|
|
$
|
10.43
|
|
|
|
6.4
|
|
|
$
|
1.5
|
|
|
Options granted
|
|
|
2,003,600
|
|
|
|
6.01
|
|
|
|
|
|
|
|
|
|
|
Options exercised
|
|
|
(286,479
|
)
|
|
|
6.10
|
|
|
|
|
|
|
|
|
|
|
Options canceled
|
|
|
(976,130
|
)
|
|
|
22.37
|
|
|
|
|
|
|
|
|
|
|
Balances, December 31, 2019
|
|
|
4,743,990
|
|
|
$
|
6.37
|
|
|
|
8.2
|
|
|
$
|
36.5
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Vested and expected to vest
December 31, 2019
|
|
|
4,743,990
|
|
|
$
|
6.37
|
|
|
|
8.2
|
|
|
$
|
36.5
|
|
|
Exercisable at December 31, 2019
|
|
|
1,779,916
|
|
|
$
|
5.98
|
|
|
|
7.0
|
|
|
$
|
14.6
|
|
|
| Stock Options Outstanding and Exercisable by Exercise Price |
At December 31, 2019, 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
|
|
|
$
|
0.42 - 1.85
|
|
|
478,366
|
|
|
|
3.80
|
|
|
$
|
1.07
|
|
|
|
475,308
|
|
|
$
|
1.06
|
|
|
$
|
4.04 - 4.28
|
|
|
6,681
|
|
|
|
7.72
|
|
|
$
|
4.22
|
|
|
|
4,191
|
|
|
$
|
4.20
|
|
|
$
|
4.66 - 4.66
|
|
|
1,030,126
|
|
|
|
9.11
|
|
|
$
|
4.66
|
|
|
|
105,638
|
|
|
$
|
4.66
|
|
|
$
|
4.74 - 5.81
|
|
|
428,825
|
|
|
|
8.93
|
|
|
$
|
5.06
|
|
|
|
73,716
|
|
|
$
|
5.16
|
|
|
$
|
6.31 - 6.31
|
|
|
1,227,849
|
|
|
|
8.41
|
|
|
$
|
6.31
|
|
|
|
531,659
|
|
|
$
|
6.31
|
|
|
$
|
6.54 - 8.21
|
|
|
537,662
|
|
|
|
8.78
|
|
|
$
|
7.63
|
|
|
|
123,674
|
|
|
$
|
8.03
|
|
|
$
|
8.35 - 9.28
|
|
|
134,450
|
|
|
|
9.56
|
|
|
$
|
8.53
|
|
|
|
7,499
|
|
|
$
|
9.24
|
|
|
$
|
9.40 - 9.40
|
|
|
537,500
|
|
|
|
7.77
|
|
|
$
|
9.40
|
|
|
|
348,437
|
|
|
$
|
9.40
|
|
|
$
|
10.78 - 61.27
|
|
|
360,713
|
|
|
|
8.71
|
|
|
$
|
12.58
|
|
|
|
107,976
|
|
|
$
|
13.22
|
|
|
$
|
70.29 - 70.29
|
|
|
1,818
|
|
|
|
2.37
|
|
|
$
|
70.29
|
|
|
|
1,818
|
|
|
$
|
70.29
|
|
|
$
|
0.42 - 70.29
|
|
|
4,743,990
|
|
|
|
8.16
|
|
|
|
|
|
|
|
1,779,916
|
|
|
$
|
5.98
|
|
|
| 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):
|
|
|
Years Ended December 31,
|
|
|
|
|
2019
|
|
|
2018
|
|
|
Stock-based compensation expense:
|
|
|
|
|
|
|
|
|
|
Research and development
|
|
$
|
2,398
|
|
|
$
|
1,192
|
|
|
General and administrative
|
|
|
3,461
|
|
|
|
2,800
|
|
|
|
|
$
|
5,859
|
|
|
$
|
3,992
|
|
|
| Weighted-Average Fair Value Valuation Assumptions |
The fair value of employee stock options was estimated using the following weighted-average assumptions for the years ended December 31, 2019 and 2018:
|
|
|
Years Ended December 31,
|
|
|
|
|
2019
|
|
|
2018
|
|
|
Employee Stock Options
|
|
|
|
|
|
|
|
|
|
Risk-free interest rate
|
|
|
2.37
|
%
|
|
|
2.79
|
%
|
|
Expected life (in years)
|
|
|
6.08
|
|
|
|
6.03
|
|
|
Dividend yield
|
|
|
—
|
|
|
|
—
|
|
|
Volatility
|
|
|
108.70
|
%
|
|
|
107.15
|
%
|
|
Weighted-average fair value of stock options granted
|
|
$
|
5.00
|
|
|
$
|
5.79
|
|
|