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Share Based Payments - Summary of Non-Employee Stock Options Accounted for As Derivative Financial Instruments (Details) - Non-employee Stock Options - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |
Fair value of non-employee stock options at beginning of year | $ 2,637 | $ 1,617
Exercise of non-employee options | (737) | (156)
Cancelled |  | (294)
Foreign exchange gains | (38) |
Change in fair value of non-employee stock options during the year | (656) | 1,470
Reclassification to additional paid-in capital | $ (1,206) |
Fair value of non-employee stock options at end of year |  | $ 2,637

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- Definition Share based compensation arrangement by share based payment award options vested in period cancelled. + References No definition available. + Details
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- Definition Share based compensation arrangement by share based payment award options vested in period exercised. + References No definition available. + Details
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- Definition Share based compensation arrangement by share based payment award options vested in period reclassification to additional paid in capital. + References No definition available. + Details
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