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STOCK PLANS AND SHARE BASED COMPENSATION (Tables) | 12 Months Ended
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Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Summary of stock-based compensation expense [Table Text Block] | The following table summarizes the stock-based compensation expense recognized in accordance with ASC 718-10 for the years ended December 31, 2017, 2016 and 2015:
| Year Ended December 31,
(in thousands) | 2017 |  | 2016 |  | 2015
Cost of revenues | $ | 1,321 |  |  | $ | 1,148 |  |  | $ | 933 |
Research and development | 8,496 |  |  | 7,309 |  |  | 5,255 |
Sales and marketing | 5,197 |  |  | 4,489 |  |  | 3,644 |
General and administrative | 9,663 |  |  | 7,939 |  |  | 4,935 |
Total stock-based compensation expense | $ | 24,677 |  |  | $ | 20,885 |  |  | $ | 14,767 |
Schedule of Unrecognized Compensation Cost, Nonvested Awards [Table Text Block] | The following table summarizes total compensation expense related to unvested awards not yet recognized, net of expected forfeitures, and the weighted average period over which it is expected to be recognized as of December 31, 2017:
| Unrecognized Compensation Expense for Unvested Awards (in thousands) |  | Weighted Average Remaining Recognition Period (in years)
Long-term performance-based awards | $ | 3,519 |  |  | 1.36
Restricted stock units | 35,132 |  |  | 3.73
Purchase plan | 128 |  |  | 0.08
Total unrecognized compensation expense | $ | 38,779 |  |  |
Fair value assumptions for employees' stock purchase rights under the Purchase Plan [Table Text Block] | The fair value of employees’ stock purchase rights under the Purchase Plan was estimated using the Black-Scholes model with the following weighted-average assumptions used during the three years ended December 31, 2017, 2016 and 2015:
| Year Ended December 31,
| 2017 |  | 2016 |  | 2015
Risk-free interest rates | 0.91% |  | 0.44% |  | 0.13%
Expected volatility rates | 30% |  | 32% |  | 29%
Expected dividend yield | 0.80% |  | 0.96% |  | 1.08%
Expected term of purchase rights (in years) | 0.50 |  | 0.50 |  | 0.50
Weighted-average estimated fair value of purchase rights | $16.74 |  | $12.23 |  | $10.18
Summary of option activity under the Plans [Table Text Block] | A summary of stock options outstanding as of December 31, 2017, and activity during three years then ended, is presented below:
(shares and intrinsic value in thousands) | Shares |  | Weighted Average Exercise Price |  | Weighted Average Remaining Contractual Term (in years) |  | Aggregate Intrinsic Value
Outstanding at January 1, 2015 | 1,344 |  |  | $ | 27.27 |  |  |  |  |
Granted | — |  |  | — |  |  |  |  |
Exercised | (311 | ) |  | $ | 26.11 |  |  |  |  |
Forfeited or expired | (3 | ) |  | $ | 37.97 |  |  |  |  |
Outstanding at December 31, 2015 | 1,030 |  |  | $ | 27.58 |  |  |  |  |
Granted | — |  |  | — |  |  |  |  |
Exercised | (333 | ) |  | $ | 25.41 |  |  |  |  |
Forfeited or expired | — |  |  | — |  |  |  |  |
Outstanding at December 31, 2016 | 697 |  |  | $ | 28.62 |  |  |  |  |
Granted | — |  |  | — |  |  |  |  |
Exercised | (186 | ) |  | $ | 27.48 |  |  |  |  |
Forfeited or expired | — |  |  | — |  |  |  |  |
Outstanding at December 31, 2017 | 511 |  |  | $ | 29.03 |  |  | 2.05 |  | $ | 22,770 |
Vested and Exercisable at December 31, 2017 | 511 |  |  |  |  | 2.05 |  | $ | 22,770 |
Summary of stock options outstanding by exercise price range [Table Text Block] | The following table summarizes the stock options outstanding at December 31, 2017:
|  | Options Outstanding |  | Options Exercisable
(shares in thousands) Range of Exercise Prices |  | Options Outstanding |  | Weighted Average Remaining Contractual Term (in years) |  | Weighted Average Exercise Price |  | Options Exercisable |  | Weighted Average Exercise Price
$17.75 - $24.21 |  | 263 |  |  | 1.26 |  | $ | 20.96 |  |  | 263 |  |  | $ | 20.96 |
$31.15 - $42.88 |  | 248 |  |  | 2.88 |  | $ | 37.56 |  |  | 248 |  |  | $ | 37.56 |
|  | 511 |  |  | 2.05 |  | $ | 29.03 |  |  | 511 |  |  | $ | 29.03 |
Summary of restricted stock units outstanding [Table Text Block] | A summary of RSU awards outstanding as of December 31, 2017, and activity during the three years then ended, is presented below:
(shares and intrinsic value in thousands) | Shares |  | Weighted Average Grant Date Fair Value Per Share |  | Weighted Average Remaining Contractual Term (in years) |  | Aggregate Intrinsic Value
Outstanding at January 1, 2015 | 692 |  |  | $ | 43.86 |  |  |  |  |
Granted | 319 |  |  | $ | 49.75 |  |  |  |  |
Vested | (267 | ) |  | $ | 42.49 |  |  |  |  |
Forfeited | (63 | ) |  | $ | 45.71 |  |  |  |  |
Outstanding at December 31, 2015 | 681 |  |  | $ | 46.98 |  |  |  |  |
Granted | 331 |  |  | $ | 46.70 |  |  |  |  |
Vested | (270 | ) |  | $ | 45.13 |  |  |  |  |
Forfeited | (24 | ) |  | $ | 47.21 |  |  |  |  |
Outstanding at December 31, 2016 | 718 |  |  | $ | 47.54 |  |  |  |  |
Granted | 558 |  |  | $ | 60.82 |  |  |  |  |
Vested | (284 | ) |  | $ | 46.52 |  |  |  |  |
Forfeited | (44 | ) |  | $ | 50.89 |  |  |  |  |
Outstanding at December 31, 2017 | 948 |  |  | $ | 55.51 |  |  | 1.97 |  | $ | 69,742 |
Outstanding and expected to vest at December 31, 2017 | 860 |  |  |  |  | 1.80 |  | $ | 63,289 |
Performance Based Awards [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Summary of performance-based awards outstanding [Table Text Block] | A summary of PSU awards outstanding as of December 31, 2017, and activity during the three years then ended, is presented below:
(shares and intrinsic value in thousands) | Shares |  | Weighted Average Grant Date Fair Value Per Share |  | Weighted Average Remaining Contractual Term (in years) |  | Aggregate Intrinsic Value
Outstanding at January 1, 2015 | — |  |  | — |  |  |  |  |
Granted | 89 |  |  | $ | 52.36 |  |  |  |  |
Vested | — |  |  | — |  |  |  |  |
Forfeited or canceled | (78 | ) |  | $ | 52.35 |  |  |  |  |
Outstanding at December 31, 2015 | 11 |  |  | $ | 52.35 |  |  |  |  |
Granted | 101 |  |  | $ | 46.26 |  |  |  |  |
Vested | (11 | ) |  | $ | 52.35 |  |  |  |  |
Forfeited or canceled | (2 | ) |  | $ | 46.87 |  |  |  |  |
Outstanding at December 31, 2016 | 99 |  |  | $ | 46.25 |  |  |  |  |
Granted | 88 |  |  | $ | 63.99 |  |  |  |  |
Vested | (99 | ) |  | $ | 46.25 |  |  |  |  |
Forfeited or canceled | (9 | ) |  | $ | 63.99 |  |  |  |  |
Outstanding at December 31, 2017 | 79 |  |  | $ | 63.99 |  |  | 0 |  | $ | 5,819 |
Outstanding and expected to vest at December 31, 2017 | 79 |  |  |  |  | 0 |  | $ | 5,819 |
Long-Term Performance-based Awards [Member] |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
Summary of performance-based awards outstanding [Table Text Block] | A summary of PRSU awards outstanding as of December 31, 2017, and activity during the three years then ended, is presented below:
(shares and intrinsic value in thousands) | Shares |  | Weighted Average Grant Date Fair Value Per Share |  | Weighted Average Remaining Contractual Term (in years) |  | Aggregate Intrinsic Value
Outstanding at January 1, 2015 | 61 |  |  | $ | 55.51 |  |  |  |  |
Granted | 72 |  |  | $ | 52.47 |  |  |  |  |
Vested | — |  |  | — |  |  |  |  |
Forfeited or canceled | (4 | ) |  | $ | 57.76 |  |  |  |  |
Outstanding at December 31, 2015 | 129 |  |  | $ | 53.75 |  |  |  |  |
Granted | 78 |  |  | $ | 43.26 |  |  |  |  |
Vested | — |  |  | — |  |  |  |  |
Forfeited or canceled | (57 | ) |  | $ | 55.35 |  |  |  |  |
Outstanding at December 31, 2016 | 150 |  |  | $ | 47.65 |  |  |  |  |
Granted | 71 |  |  | $ | 63.00 |  |  |  |  |
Vested | — |  |  | — |  |  |  |  |
Forfeited or canceled | (37 | ) |  | $ | 51.59 |  |  |  |  |
Outstanding at December 31, 2017 | 184 |  |  | $ | 52.80 |  |  | 1.49 |  | $ | 13,547 |
Outstanding and expected to vest at December 31, 2017 | 164 |  |  |  |  | 1.28 |  | $ | 12,072 |

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