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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
	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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