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Share-Based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2018
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Summary of Performance-Based RSU | The following table lists the inputs to the model used for the PSUs granted in 2018 and 2017:
|  | Year ended December 31, 2018 |  |  | Year ended December 31, 2017 |
Fair value at grant date (in euros) |  |  | 15.31 |  |  |  | 11.52 |
Share price at grant date (in euros) |  |  | 10.27 |  |  |  | 7.50 |
Dividend yield |  |  | — |  |  |  | — |
Expected volatility(A) |  |  | 75% |  |  |  | 75% |
Risk-free interest rate (US government bond yield) |  |  | 2.60% |  |  |  | 1.51% |
Model used |  |  | Monte Carlo |  |  |  | Monte Carlo |
(A) | Volatilities for the Company and companies included in indices were estimated based on observed historical volatilities over period equal to PSU vesting period.
Summary of Movements in Shares | The following table illustrates the number and movements in shares during the year:
|  | Performance-Based RSU |  |  | Restricted Stock Units |  |  | Equity Award Plans |
|  | Potential Shares |  |  | Weighted-Average Grant-Date Fair Value per Share |  |  | Potential Shares |  |  | Weighted-Average Grant-Date Fair Value per Share |  |  | Potential Shares |  |  | Weighted-Average Grant-Date Fair Value per Share |
At January 1, 2017 |  |  | 2,066,835 |  |  | € | 7.50 |  |  |  | 479,500 |  |  | € | 7.82 |  |  |  | 94,881 |  |  | € | 5.01 |
Granted(A) |  |  | 892,781 |  |  | € | 11.52 |  |  |  | 703,180 |  |  | € | 7.50 |  |  |  | 54,409 |  |  | € | 6.09 |
Over-performance(B) |  |  | 552,728 |  |  | € | 7.63 |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | — |
Vested |  |  | — |  |  |  | — |  |  |  | (125,000 | ) |  | € | 7.02 |  |  |  | (53,950 | ) |  | € | 5.76 |
Forfeited(C) |  |  | (254,504 | ) |  | € | 8.29 |  |  |  | (113,180 | ) |  | € | 7.27 |  |  |  | — |  |  |  | — |
At December 31, 2017 |  |  | 3,257,840 |  |  | € | 8.56 |  |  |  | 944,500 |  |  | € | 7.76 |  |  |  | 95,340 |  |  | € | 5.20 |
Granted(A) |  |  | 701,109 |  |  | € | 15.31 |  |  |  | 595,687 |  |  | € | 10.23 |  |  |  | 30,709 |  |  | € | 10.27 |
Over-performance(B) |  |  | 633,670 |  |  | € | 7.28 |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | — |
Vested |  |  | (1,265,635 | ) |  | € | 7.09 |  |  |  | (155,000 | ) |  | € | 10.83 |  |  |  | (68,136 | ) |  | € | 4.85 |
Forfeited(C) |  |  | (241,820 | ) |  | € | 8.40 |  |  |  | (72,663 | ) |  | € | 8.57 |  |  |  | — |  |  |  | — |
At December 31, 2018 |  |  | 3,085,164 |  |  | € | 10.45 |  |  |  | 1,312,524 |  |  | € | 8.47 |  |  |  | 57,913 |  |  | € | 8.31 |
(A) | For PSUs, the number of potential shares granted is presented using a vesting multiplier of 100%.
(B) | When the achievement of TSR performance exceeds the vesting multiplier of 100%, the additional potential shares are presented as over-performance shares.
(C) | For potential shares related to PSUs, 213,820 were forfeited following the departure of certain beneficiaries and 28,000 were forfeited in relation to the non-fulfilment of performance conditions.

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- Definition Disclosure of number of other equity instruments. + References No definition available. + Details
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- Definition The disclosure of information about indirect, by reference to the fair value of the equity instruments granted, measurement of the fair value of goods or services received as consideration for the entity's other equity instruments (ie other than share options). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2018-01-01 -Paragraph 47 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2018-03-01&anchor=para_47_b&doctype=Standard -URIDate 2018-03-16 + Details
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