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Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Summary of Share Option Activity

Share option activity under the 2014 Plan is summarized as follows:

		Number of Shares				Weighted- Average Exercise Price				Weighted-Average Remaining Contractual Term (in years)				Aggregate Intrinsic Value (in thousands)(1)
Outstanding as of January 1, 2018			3,767,130			$	12.69
Granted			830,420			44.77
Exercised			(507,632	)		10.07
Forfeited or cancelled			(73,328	)		19.93
Outstanding as of December 31, 2018			4,016,590			$	19.47				7.24			$	93,520
Options exercisable as of December 31, 2018			2,451,584			$	10.11				6.51			$	78,280
Options unvested as of December 31, 2018			1,565,006			$	34.14				8.39			$	15,240

(1) The aggregate intrinsic value of options is calculated as the difference between the exercise price of the share options and the fair value of the Company’s ordinary shares for those share options that had exercise prices lower than the fair value of the ordinary shares as of the end of the period.

Summary of RSU Activity

RSU activity for the year ended December 31, 2018 is summarized as follows:

		RSUs				Average Grant Date Fair Value (in dollars per share)
Outstanding as of January 1, 2018			154,459				29.05
Granted			313,747				40.17
Vested			(38,594	)			26.30
Forfeited			(21,091	)			37.27
RSUs Outstanding at December 31, 2018			408,521			$	37.16

Summary of Share-based Compensation Expense Classified in Consolidated Statements of Operations and Comprehensive Loss

Share-based compensation expense for the years ended December 31, 2018, 2017 and 2016 is classified as operating expenses in the consolidated statements of operations and comprehensive loss as follows:

		For the Year Ended December 31,
		2018				2017				2016
		(in thousands)
Research and development expenses		$	9,172			$	7,670			$	4,936
General and administrative expenses			6,424				4,473				1,911
Total share-based compensation expense		$	15,596			$	12,143			$	6,847

Employee Stock Option [Member]

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Summary of Fair Value of Share Options Granted

The assumptions used in the Black-Scholes option pricing model to determine the fair value of share options granted to employees during the period were as follows:

		For the Year Ended December 31,
		2018		2017		2016
Risk-free interest rate		2.49% – 3.01%		1.49% – 2.23%		1.15% – 2.18%
Expected term (in years)		3.00 – 6.25		3.00 – 6.25		3.00 – 6.25
Expected volatility		64.17% – 70.90%		68.95% – 72.24%		60.89% – 68.76%
Expected dividend yield		0%		0%		0%

X

- Definition

Tabular disclosure of the allocation of equity-based compensation costs to a given line item on the balance sheet and income statement for the period. This may include the reporting line for the costs and the amount capitalized and expensed.

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Tabular disclosure of the number and weighted-average grant date fair value for restricted stock units that were outstanding at the beginning and end of the year, and the number of restricted stock units that were granted, vested, or forfeited during the year.

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