Quarterly report pursuant to Section 13 or 15(d)

Stock Plans (Tables)

v3.8.0.1
Stock Plans (Tables)
 3 Months Ended
Mar. 31, 2018
Stock Plans [Abstract]  
Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block]
The following table summarizes the stock-based compensation expense recorded for awards under the stock option plans for the three month periods ended March 31, 2018 and 2017:
 
 
 
Three Months Ended 
March 31,
 
(in thousands, except per share amounts)
 
2018
 
2017
 
Research and development
 
$
163
 
$
117
 
General and administrative
 
 
269
 
 
304
 
 
 
 
 
 
 
 
 
Total stock-based compensation expenses
 
$
432
 
$
421
 
Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions [Table Text Block]
We use the Black-Scholes-Merton option-pricing model with the following assumptions to estimate the stock-based compensation expense for the three month period ended March 31, 2018 and 2017:
 
 
 
Three Months Ended 
March 31,
 
 
 
2018
 
2017
 
Weighted-average risk-free interest rate
 
 
2.75
%
 
2.16
%
Expected dividend payments
 
 
—
 
 
—
 
Expected holding period (years)1
 
 
6.4
 
 
6.6
 
Weighted-average volatility factor2
 
 
0.89
 
 
0.88
 
Estimated forfeiture rates for options granted3
 
 
26
%
 
28
%
   
(1)
Expected holding period is based on historical experience of similar awards, giving consideration to the contractual terms of the stock-based awards, vesting schedules and the expectations of future employee behavior.
 
(2)
Weighted average volatility is based on the historical volatility of our common stock.
 
(3)
Estimated forfeiture rates are based on historical data.
Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block]
The following table summarizes option activity for the three month period ended March 31, 2018:
 
(in thousands, except per share amounts)
 
Options
 
Weighted 
Average 
Exercise 
Price
 
Weighted
Average 
Remaining 
Option 
Term
 
Aggregate 
Intrinsic 
Value
 
Outstanding at January 1, 2018
 
 
2,728
 
$
4.32
 
 
5.75
 
$
30
 
Granted
 
 
945
 
 
0.97
 
 
 
 
 
 
 
Exercised
 
 
—
 
 
—
 
 
 
 
 
 
 
Expired or cancelled
 
 
—
 
 
—
 
 
 
 
 
 
 
Forfeited
 
 
—
 
 
—
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Outstanding at March 31, 2018
 
 
3,673
 
$
3.46
 
 
6.64
 
$
76
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Exercisable at March 31, 2018
 
 
2,416
 
$
4.48
 
 
5.67
 
$
19