Stock Plans and Stock Based Compensation (Tables)
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12 Months Ended |
Dec. 31, 2015 |
|---|
| Summary of Stock Option Activity |
A summary of
stock option activity under the Amended and Restated 2010 Plan, the
2000 Stock Incentive Plan and the 2000 Director Stock Option Plan
is summarized as follows:
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Number of
Shares |
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Weighted
Average
Exercise
Price per
Share |
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Outstanding,
December 31, 2014 (7,534,372 exercisable at weighted average
price of $2.45 per share)
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|
11,319,619 |
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|
$ |
2.66 |
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Granted
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3,228,250 |
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|
2.33 |
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Exercised
|
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|
(695,338 |
) |
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|
1.63 |
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Cancelled
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|
(561,907 |
) |
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|
3.63 |
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Outstanding,
December 31, 2015 (7,946,442 exercisable at weighted average
price of $2.58 per share)
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13,290,624 |
|
|
$ |
2.60 |
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Vested and unvested
expected to vest
|
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|
12,697,446 |
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$ |
2.60 |
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| Summary of Compensation Expense Related to ESPP |
For the years
ended December 31, 2015, 2014 and 2013, the Company recorded
compensation expense related to its ESPP and calculated the fair
value of shares expected to be purchased under the ESPP using the
Black-Scholes models with the following assumptions:
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For the Year Ended
December 31, |
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2015 |
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|
2014 |
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|
2013 |
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|
Compensation expense
recognized under ESPP
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|
$ |
29,924 |
|
|
$ |
25,604 |
|
|
$ |
40,008 |
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Expected term
|
|
|
6 months |
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|
6 months |
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|
6 months |
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Risk-free interest
rate
|
|
|
0.06-0.5 |
% |
|
|
0.06-0.09 |
% |
|
|
0.08-0.1 |
% |
|
Volatility
|
|
|
55-78 |
% |
|
|
55-66 |
% |
|
|
42-66 |
% |
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Dividends
|
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|
None |
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|
None |
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|
None |
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| Employee and Non-Employee Share Based Compensation Expense Allocation |
For the years
ended December 31, 2015, 2014 and 2013, the Company recorded
employee and non-employee stock-based compensation expense to the
following line items in its Costs and Expenses section of the
Consolidated Statements of Operations and Comprehensive
Loss:
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For the Year Ended
December 31, |
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2015 |
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|
2014 |
|
|
2013 |
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Research and development
expenses
|
|
$ |
1,023,269 |
|
|
$ |
671,063 |
|
|
$ |
879,052 |
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|
General and administrative
expenses
|
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|
2,851,977 |
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|
2,388,926 |
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|
2,123,189 |
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Total stock-based
compensation expense
|
|
$ |
3,875,246 |
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|
$ |
3,059,989 |
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|
$ |
3,002,241 |
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| Vesting Tied to Service Conditions [Member] |
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| Valuation Assumptions Used to Calculate Fair Value of Employee Options Awarded |
The
Black-Scholes option pricing model employs the following key
assumptions for employee and director options awarded during each
of the following years:
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For the Year Ended
December 31, |
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2015 |
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|
2014 |
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|
2013 |
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Expected term
(years)—Employees
|
|
|
6.0 |
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|
6.0 |
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|
6.0 |
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Expected term
(years)—Officers and Directors
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|
7.0 |
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|
7.0 |
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|
7.0 |
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Risk-free interest
rate
|
|
|
1.5-1.9 |
% |
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|
1.9 |
% |
|
|
1.0-2.1 |
% |
|
Expected
volatility
|
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|
68-70 |
% |
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|
70-71 |
% |
|
|
70-72 |
% |
|
Expected dividend
yield
|
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|
None |
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|
None |
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|
None |
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| Vesting Tied to Market Conditions [Member] |
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| Valuation Assumptions Used to Calculate Fair Value of Employee Options Awarded |
The key
assumptions used in these Monte Carlo simulation models and
resulting valuations are noted in the following table:
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Market
Condition
Options
Granted
February 18,
2014 |
|
Market
Condition
Options
Granted
June 2,
2014 |
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Expected life
(years)—officers
|
|
6 |
|
6 |
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Risk-free interest
rate
|
|
1.9% |
|
2.1% |
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Volatility
|
|
70% |
|
65% |
|
Dividends
|
|
None |
|
None |
|
Number of options
granted
|
|
640,000 |
|
400,000 |
|
Fair value per
share
|
|
$1.20 |
|
$0.34 |
|