Stock Plans (Tables)
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12 Months Ended |
Dec. 31, 2017 |
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| Stock Plans [Abstract] |
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| Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block] |
Activity under our stock plans, as well as non-plan activity, is summarized below (shares in thousands): | | | Shares or
Awards Available
For Grant | | Number of
Options and
Awards
Outstanding | | Weighted Average
Exercise Price | | | Balance at December 31, 2014 | | | 282 | | | 1,269 | | $ | 6.40 | | | Increase in shares reserved | | | 1,364 | | | — | | | — | | | Options granted | | | (700) | | | 700 | | $ | 4.46 | | | Options expired | | | — | | | (20) | | $ | 13.27 | | | Awards issued | | | — | | | (66) | | $ | — | | | Termination of option plan | | | (32) | | | — | | $ | — | | | Balance at December 31, 2015 | | | 914 | | | 1,883 | | $ | 5.83 | | | Increase in shares reserved | | | 1,136 | | | — | | | — | | | Options granted | | | (168) | | | 168 | | $ | 5.10 | | | Options exercised | | | — | | | (8) | | $ | 3.37 | | | Options expired | | | — | | | (41) | | $ | 10.85 | | | Balance at December 31, 2016 | | | 1,882 | | | 2,002 | | $ | 5.67 | | | Options granted | | | (946) | | | 946 | | $ | 2.55 | | | Options cancelled | | | 60 | | | (114) | | $ | 5.27 | | | Options expired | | | — | | | (106) | | $ | 13.11 | | | Balance at December 31, 2017 | | | 996 | | | 2,728 | | $ | 4.32 | |
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| Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block] |
Options to purchase approximately 2.1 million and 1.7 million shares were exercisable at December 31, 2017 and 2016, respectively. The options outstanding at December 31, 2017 have been segregated into five ranges for additional disclosure as follows (options in thousands): | | | Options Outstanding | | Options Exercisable | | | Range of Exercise
Prices | | Number
Outstanding | | Weighted
Average
Remaining
Life (Years) | | Weighted
Average
Exercise Price | | Number
Exercisable | | Weighted
Average
Exercise Price | | | $1.25 - $2.89 | | | 519 | | | 5.96 | | $ | 1.42 | | | 122 | | $ | 1.37 | | | $2.90 - $3.95 | | | 666 | | | 8.28 | | $ | 3.67 | | | 458 | | $ | 3.57 | | | $3.96 - $4.72 | | | 421 | | | 1.56 | | $ | 4.33 | | | 420 | | $ | 4.33 | | | $4.73 - $5.41 | | | 588 | | | 7.99 | | $ | 5.10 | | | 574 | | $ | 5.10 | | | $5.42 - $12.98 | | | 534 | | | 3.22 | | $ | 7.07 | | | 534 | | $ | 7.07 | | | $1.25 - $12.98 | | | 2,728 | | | 5.75 | | $ | 4.32 | | | 2,108 | | $ | 4.90 | |
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| 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 years ended December 31, 2017, 2016 and 2015: | | | Years Ended December 31, | | | | | 2017 | | 2016 | | 2015 | | | Weighted-average risk-free interest rate | | | 2.13 | % | | 1.53 | % | | 1.88 | % | | Expected dividend payments | | | — | | | — | | | — | | | Expected holding period (years)(1) | | | 5.90 | | | 6.53 | | | 6.48 | | | Weighted-average volatility factor(2) | | | 0.90 | | | 0.92 | | | 1.16 | | | Estimated forfeiture rates for options granted | | | 27 | % | | 29 | % | | 30 | % | | (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. |
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| Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block] |
The following table summarizes the stock-based compensation expense and impact on our basic and diluted loss per share for the years ended December 31, 2017, 2016 and 2015: | | | Years Ended December 31, | | | (in thousands, except per share amounts) | | 2017 | | 2016 | | 2015 | | | Research and development | | $ | 519 | | $ | 386 | | $ | 341 | | | General and administrative | | | 1,168 | | | 653 | | | 685 | | | Total stock-based compensation expenses | | $ | 1,687 | | $ | 1,039 | | $ | 1,026 | | | Increase in basic net income (loss) per share | | $ | (0.08) | | $ | (0.05) | | $ | (0.05) | | | Increase in diluted net income (loss) per share | | $ | (0.08) | | $ | (0.05) | | $ | (0.05) | |
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| Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block] |
The following table summarizes option activity for the year ended December 31, 2017: | (in thousands, except per share
amounts) | | Shares | | Weighted
Average
Exercise
Price | | Weighted
Average
Remaining
Contractual
Term | | Aggregate
Intrinsic
Value | | | Outstanding at January 1, 2017 | | | 2,002 | | $ | 5.67 | | | 5.68 | | $ | 203 | | | Granted | | | 946 | | | 2.55 | | | | | | | | | Cancelled | | | (114) | | | 5.27 | | | | | | | | | Expired | | | (106) | | | 13.11 | | | | | | | | | Outstanding at December 31, 2017 | | | 2,728 | | $ | 4.32 | | | 5.75 | | $ | 30 | | | Exercisable at December 31, 2017 | | | 2,108 | | $ | 4.90 | | | 5.34 | | $ | 8 | |
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