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Stock-Based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2017
Stock-Based Compensation Expense Related to Stock Options, PSUs, RSUs and Restricted Stock | The following table summarizes stock-based compensation expense related to stock options, PSUs, RSUs and restricted stock for the years ended December 31, 2017, 2016 and 2015, which was recognized as follows:
(In thousands) |  | 2017 |  |  | 2016 |  |  | 2015 |
Stock-based compensation expense included in cost of sales |  | $ | 379 |  |  | $ | 389 |  |  | $ | 280 |
Selling, general and administrative expense |  |  | 4,063 |  |  |  | 3,341 |  |  |  | 3,261 |
Research and development expense |  |  | 2,991 |  |  |  | 2,965 |  |  |  | 3,171 |
Stock-based compensation expense included in operating expenses |  |  | 7,054 |  |  |  | 6,306 |  |  |  | 6,432 |
Total stock-based compensation expense |  |  | 7,433 |  |  |  | 6,695 |  |  |  | 6,712 |
Tax benefit for expense associated with non-qualified options, PSUs, RSUs and restricted stock |  |  | (1,699 | ) |  |  | (963 | ) |  |  | (862 | )
Total stock-based compensation expense, net of tax |  | $ | 5,734 |  |  | $ | 5,732 |  |  | $ | 5,850 |
Summary of Stock Options Outstanding | The following table is a summary of our stock options outstanding as of December 31, 2016 and 2017 and the changes that occurred during 2017:
(In thousands, except per share amounts) |  | Number of Options |  |  | Weighted Average Exercise Price |  |  | Weighted Avg. Remaining Contractual Life in Years |  |  | Aggregate Intrinsic Value |
Stock options outstanding, December 31, 2016 |  |  | 6,338 |  |  | $ | 22.14 |  |  |  | 5.63 |  |  | $ | 16,972 |
Stock options granted |  |  | — |  |  | $ | — |  |  |  |  |  |  |  |  |
Stock options exercised |  |  | (742 | ) |  | $ | 18.08 |  |  |  |  |  |  |  |  |
Stock options forfeited |  |  | (70 | ) |  | $ | 17.29 |  |  |  |  |  |  |  |  |
Stock options expired |  |  | (378 | ) |  | $ | 24.14 |  |  |  |  |  |  |  |  |
Stock options outstanding, December 31, 2017 |  |  | 5,148 |  |  | $ | 22.65 |  |  |  | 4.87 |  |  | $ | 6,109 |
Stock options vested and expected to vest, December 31, 2017 |  |  | 5,148 |  |  | $ | 22.65 |  |  |  | 4.87 |  |  | $ | 6,109 |
Stock options exercisable, December 31, 2017 |  |  | 4,351 |  |  | $ | 23.78 |  |  |  | 4.37 |  |  | $ | 3,810 |
Stock Options Outstanding | The following table further describes our stock options outstanding as of December 31, 2017:
|  | Options Outstanding |  |  | Options Exercisable |
Range of Exercise Prices |  | Options Outstanding at 12/31/17 (In thousands) |  |  | Weighted Avg. Remaining Contractual Life in Years |  |  | Weighted Average Exercise Price |  |  | Options Exercisable at 12/31/17 (In thousands) |  |  | Weighted Average Exercise Price |
$14.88 – 18.96 |  |  | 1,623 |  |  |  | 6.02 |  |  | $ | 15.77 |  |  |  | 1,063 |  |  | $ | 15.96 |
$18.97 – 23.45 |  |  | 801 |  |  |  | 6.68 |  |  | $ | 19.11 |  |  |  | 565 |  |  | $ | 19.17 |
$23.46 – 30.35 |  |  | 1,400 |  |  |  | 4.16 |  |  | $ | 23.85 |  |  |  | 1,399 |  |  | $ | 23.85 |
$30.36 – 41.92 |  |  | 1,324 |  |  |  | 3.29 |  |  | $ | 31.94 |  |  |  | 1,324 |  |  | $ | 31.94 |
|  |  | 5,148 |  |  |  |  |  |  |  |  |  |  |  | 4,351 |  |  |  |  |
Summary of PSUs, RSUs and Restricted Stock Outstanding | The following table is a summary of our PSUs, RSUs and restricted stock outstanding as of December 31, 2016 and 2017 and the changes that occurred during 2017.
(In thousands, except per share amounts) |  | Number of shares |  |  | Weighted Average Grant Date Fair Value |
Unvested PSUs, RSUs and restricted stock outstanding, December 31, 2016 |  |  | 527 |  |  | $ | 20.53 |
PSUs, RSUs and restricted stock granted |  |  | 950 |  |  | $ | 21.69 |
PSUs, RSUs and restricted stock vested |  |  | (154 | ) |  | $ | 20.84 |
PSUs, RSUs and restricted stock forfeited |  |  | (31 | ) |  | $ | 20.99 |
Unvested RSUs and restricted stock outstanding, December 31, 2017 |  |  | 1,292 |  |  | $ | 21.33 |
Stock Options [Member] |
Summary of Weighted-Average Assumptions and Value of Options Granted | There were no stock option grants in 2017. The weighted-average estimated fair value of stock options granted to employees during the years ended December 31, 2016 and 2015 was $5.22 per share and $4.28 per share, respectively, with the following weighted-average assumptions:
|  | 2016 |  |  | 2015 |
Expected volatility |  |  | 34.79 | % |  |  | 34.57 | %
Risk-free interest rate |  |  | 1.36 | % |  |  | 1.81 | %
Expected dividend yield |  |  | 1.98 | % |  |  | 2.35 | %
Expected life (in years) |  |  | 6.25 |  |  |  | 6.23 |
Performance Stock Units (PSUs) [Member] |
Summary of Weighted-Average Assumptions and Value of Options Granted | The PSU pricing model also requires the use of several significant assumptions that impact the fair value estimate. The estimated fair value of the PSUs granted to employees during the years ended December 31, 2017, 2016 and 2015 was $24.17 per share, $23.50 per share and $17.64 per share, respectively, with the following assumptions:
|  | 2017 |  |  | 2016 |  |  | 2015 |
Expected volatility |  |  | 27.03 | % |  |  | 29.79 | % |  |  | 31.34 | %
Risk-free interest rate |  |  | 1.78 | % |  |  | 1.17 | % |  |  | 1.20 | %
Expected dividend yield |  |  | 1.74 | % |  |  | 1.80 | % |  |  | 2.35 | %

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