Stock Plans (Tables) |
12 Months Ended | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Dec. 31, 2017 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Table Text Block [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Summary of Stock Option and RSA Activity | A summary of stock option and RSA/RSU activity as of December 31, 2017, and changes during the year, is presented below:
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Weighted-average remaining contractual life and aggregate intrinsic value of the Company's stock options outstanding, exerciseable, and vested and expected to vest | The weighted-average remaining contractual life and the aggregate intrinsic value (the amount by which the fair value of the Company’s stock exceeds the exercise price of the option) of the stock options outstanding, exercisable, vested, and expected to vest as of December 31, 2017, were as follows:
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Weighted Average Assumptions Used | The fair value of each option is estimated on the date of grant using a Black-Scholes-Merton option-pricing model. The following weighted-average assumptions were used for options granted in 2017, 2016 and 2015:
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Special Stock Option Assumptions [Text Block] | On October 31, 2017, certain senior executives were awarded stock options with a term of seven years, and include a three-year service condition, as well as performance and market conditions. Therefore, the fair values of these options were estimated at the grant date using a Monte Carlo Valuation model with the following assumptions:
The expected volatility is based on both weighted historical and implied volatilities of the Company’s common stock price. |
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Summary of Stock Plan Expenses | The components of the Company’s total stock-based compensation expense (net of forfeitures) for the years ended December 31 are as follows:
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