Stockholders' Equity (Tables)
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12 Months Ended |
Dec. 31, 2017 |
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| Equity [Abstract] |
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| Summary of Stock Options Activity |
The activity for stock options under the Company’s stock plans is as follows:
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Remaining
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weighted-
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Weighted-
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average
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Per share
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average
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contractual
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average
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Price per
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exercise
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terms
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intrinsic
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Options
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share
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price
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(in years)
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value
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Outstanding as of December 31, 2014
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2,261,633
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$0.60-$24.52
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$
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7.31
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6.43
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$
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24.06
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Granted
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759,301
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37.10-46.66
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39.91
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Exercised
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(676,715
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0.60-24.52
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2.39
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Forfeited
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(48,849
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0.75-38.54
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16.28
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Outstanding as of December 31, 2015
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2,295,370
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0.60-46.66
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19.36
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5.98
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21.07
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Vested and exercisable as of December 31, 2015
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933,707
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0.60-46.66
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7.16
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5.55
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32.97
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Vested and expected to vest as of December 31, 2015
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2,179,294
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0.60-46.66
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19.15
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5.96
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21.27
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Outstanding as of December 31, 2015
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2,295,370
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0.60-46.66
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19.36
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5.98
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21.07
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Granted
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683,998
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44.19-58.95
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44.70
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Exercised
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(570,079
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0.60-46.66
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12.32
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Forfeited
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(53,247
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1.17-44.19
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28.09
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Expired
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(515
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8.70
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8.70
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Outstanding as of December 31, 2016
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2,355,527
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0.60-58.95
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28.22
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5.42
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38.95
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Vested and exercisable as of December 31, 2016
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1,023,865
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0.60-46.66
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16.61
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4.96
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50.56
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Vested and expected to vest as of December 31, 2016
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2,259,811
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0.60-46.66
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27.95
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5.40
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39.22
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Outstanding as of December 31, 2016
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2,355,527
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0.60-58.95
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28.22
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5.42
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38.95
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Granted
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64,498
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83.30
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83.30
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Exercised
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(520,393
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0.60-58.95
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24.16
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Forfeited
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(63,173
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24.52-58.95
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43.74
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Expired
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(33
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8.70
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8.70
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Outstanding as of December 31, 2017
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1,836,426
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0.60-83.30
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30.77
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4.58
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88.31
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Vested and exercisable as of December 31, 2017
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1,176,504
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0.60-83.30
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24.33
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4.39
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94.75
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Vested and expected to vest as of December 31, 2017
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1,792,871
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$0.60-$83.30
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$
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30.50
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4.58
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$
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88.58
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| Summary of Restricted Stock Activity |
Stock Awards activity for the year ended December 31, 2017 is summarized below:
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Weighted-
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average
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grant
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Performance
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date fair
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and
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value
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Time-based
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time-based
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Total
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per share
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Unvested restricted stock units as of December 31, 2016
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—
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—
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—
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$
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—
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Granted
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42,028
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13,109
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55,137
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90.05
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Vested
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—
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—
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—
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—
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Forfeited/canceled
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—
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—
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—
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—
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Unvested restricted stock units as of December 31, 2017
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42,028
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13,109
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55,137
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$
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90.05
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Unvested restricted stock awards outstanding as of December 31, 2016
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—
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—
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—
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$
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—
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Granted
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20,789
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20,785
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41,574
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91.52
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Vested
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—
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—
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—
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—
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Forfeited/canceled
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—
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—
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—
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—
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Unvested restricted stock awards outstanding as of December 31, 2017
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20,789
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20,785
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41,574
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$
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91.52
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Unvested and expected to vest restricted stock awards outstanding as of December 31, 2017
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17,024
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17,027
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34,051
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$
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91.52
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| Summary of Stock-based Compensation Expense |
Stock-based compensation
Stock-based compensation expense recognized for the years ended December 31, 2017, 2016 and 2015 was as follows:
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Years ended December 31,
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(amounts in thousands)
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2017
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2016
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2015
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Stock-based compensation expense by type of award:
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Stock option plan awards
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$
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7,652
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$
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6,850
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$
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3,280
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Restricted stock units and restricted stock awards
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1,447
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—
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—
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Employee stock purchase plan
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541
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444
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360
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Total stock-based compensation expense
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$
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9,640
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$
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7,294
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$
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3,640
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For the years ended December 31, 2017, 2016 and 2015, stock-based compensation expense recognized under ASC 718, included in cost of revenues, sales and marketing expense, general and administrative expense, and research and development expense was as follows:
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Years ended December 31,
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(amounts in thousands)
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2017
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2016
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2015
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Cost of revenue
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$
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845
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$
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639
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$
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433
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Research and development
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1,015
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776
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431
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Sales and marketing
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1,558
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1,142
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1,009
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General and administrative
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6,222
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4,737
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1,767
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Total stock-based compensation expense
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$
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9,640
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$
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7,294
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$
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3,640
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| Assumptions Used to Estimate Fair Value of Employee Options |
The value of employee options was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions used:
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2017
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2016
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2015
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Expected term (years)
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3.54-4.00
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3.54-5.48
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3.50-5.48
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Risk free interest rate
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1.65-1.73%
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1.00-1.40%
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0.95-1.77%
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Expected dividend yield
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None
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None
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None
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Volatility
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41.61-42.15%
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43.95-45.93%
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41.99-44.87%
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