Equity Incentive Plans, Employee Stock Purchase Plan and Stock-Based Compensation (Tables)
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6 Months Ended |
Jun. 30, 2020 |
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| Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] |
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| Summary of Option Activity |
The following table summarizes option activity under the Company’s 2004 Plan and 2018 Plan:
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|
|
Shares
|
|
|
Weighted-
Average
Exercise Price
|
|
|
Weighted-
Average
Remaining
Contract Term
(Years)
|
|
|
Aggregate
Intrinsic Value
(in thousands)
|
|
|
Stock options outstanding at December 31, 2019
|
|
|
3,872,664
|
|
|
$
|
12.89
|
|
|
|
7.88
|
|
|
$
|
2,119
|
|
|
Granted
|
|
|
1,496,806
|
|
|
$
|
8.88
|
|
|
|
|
|
|
|
|
|
|
Exercised
|
|
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(14,194
|
)
|
|
$
|
4.50
|
|
|
|
|
|
|
|
|
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|
Canceled and forfeited
|
|
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(46,037
|
)
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|
$
|
10.58
|
|
|
|
|
|
|
|
|
|
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Stock options outstanding at June 30, 2020
|
|
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5,309,239
|
|
|
$
|
11.80
|
|
|
|
8.03
|
|
|
$
|
1,286
|
|
|
Stock options exercisable at June 30, 2020
|
|
|
2,226,316
|
|
|
$
|
12.53
|
|
|
|
6.74
|
|
|
$
|
630
|
|
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| 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:
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Six Months Ended
|
|
|
|
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June 30,
|
|
|
|
|
2020
|
|
|
2019
|
|
|
Expected term (in years)
|
|
2.84-7.01
|
|
|
5.03-7.01
|
|
|
Expected volatility
|
|
73.15%-83.96%
|
|
|
72.89%-74.89%
|
|
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Risk-free interest rate
|
|
0.16%-1.62%
|
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1.85%-2.55%
|
|
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Expected dividend
|
|
|
–
|
|
|
|
–
|
|
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| Summary of Status and Activity of Non-vested RSUs |
A summary of the status and activity of non-vested RSUs at June 30, 2020 is as follows:
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Number of
shares
|
|
|
Weighted
Average
Grant-Date
Fair Value
|
|
|
Non-vested December 31, 2019
|
|
|
335,799
|
|
|
$
|
13.49
|
|
|
Granted
|
|
|
497,250
|
|
|
$
|
8.19
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|
|
Vested and released
|
|
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(41,300
|
)
|
|
$
|
11.44
|
|
|
Canceled and forfeited
|
|
|
(16,758
|
)
|
|
$
|
9.64
|
|
|
Non-vested June 30, 2020
|
|
|
774,991
|
|
|
$
|
10.28
|
|
|
| Schedule of Fair Value of ESPP Shares Using Option Pricing Model |
For the six months ended June 30, 2020, the fair value of ESPP shares was estimated using the following assumptions:
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Six Months Ended
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June 30,
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|
2020
|
|
|
2019
|
|
|
Expected term (in years)
|
0.5
|
|
|
0.5
|
|
|
Expected volatility
|
|
63.04
|
%
|
|
|
74.41
|
%
|
|
Risk-free interest rate
|
|
1.92
|
%
|
|
|
2.09
|
%
|
|
Expected dividend
|
|
–
|
|
|
|
–
|
|
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| Schedule of Stock-Based Compensation Expense Recognized |
Total stock-based compensation expense recognized was as follows:
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Three Months Ended
|
|
|
Six Months Ended
|
|
|
|
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June 30,
|
|
|
June 30,
|
|
|
|
|
2020
|
|
|
2019
|
|
|
2020
|
|
|
2019
|
|
|
|
|
(in thousands)
|
|
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(in thousands)
|
|
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Research and development expense:
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|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
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Stock options
|
|
$
|
340
|
|
|
$
|
246
|
|
|
$
|
584
|
|
|
$
|
474
|
|
|
Restricted stock units
|
|
|
243
|
|
|
|
196
|
|
|
|
407
|
|
|
|
303
|
|
|
ESPP
|
|
|
113
|
|
|
|
-
|
|
|
|
220
|
|
|
|
76
|
|
|
Subtotal
|
|
|
696
|
|
|
|
442
|
|
|
|
1,211
|
|
|
|
853
|
|
|
General and administrative expense:
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Stock options
|
|
|
1,756
|
|
|
|
1,654
|
|
|
|
3,458
|
|
|
|
3,154
|
|
|
Restricted stock units
|
|
|
528
|
|
|
|
367
|
|
|
|
989
|
|
|
|
714
|
|
|
ESPP
|
|
|
31
|
|
|
|
-
|
|
|
|
60
|
|
|
|
28
|
|
|
Subtotal
|
|
|
2,315
|
|
|
|
2,021
|
|
|
|
4,507
|
|
|
|
3,896
|
|
|
Total
|
|
$
|
3,011
|
|
|
$
|
2,463
|
|
|
$
|
5,718
|
|
|
$
|
4,749
|
|
|
|
|
|
|
|
|
|
|
|
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|
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| Summary of the Status of Call Options |
A summary of the status of the call options at June 30, 2020 and at December 31, 2019 is as follows:
|
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|
June 30,
|
|
|
December 31,
|
|
|
|
|
2020
|
|
|
2019
|
|
|
|
|
Shares
|
|
|
Shares
|
|
|
Options vested and exercised
|
|
|
191,165
|
|
|
|
191,165
|
|
|
Options vested and outstanding
|
|
|
66,685
|
|
|
|
-
|
|
|
Options unvested and outstanding
|
|
|
8,890
|
|
|
|
75,475
|
|
|
Total options granted
|
|
|
266,740
|
|
|
|
266,640
|
|
|