Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

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

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, 2017		3,577,766		$	10.58
Granted		522,750		26.33
Exercised		(137,493	)	6.74
Forfeited or cancelled		(195,893	)	14.71
Outstanding as of December 31, 2017		3,767,130		$	12.69		7.81	$	84,675
Options exercisable as of December 31, 2017		2,257,455		$	7.64		7.43	$	62,060
Options unvested as of December 31, 2017		1,509,675		$	20.23		8.37	$	22,614

(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 years ended December 31, 2017 and 2016 is summarized as follows:

	RSUs			Average Grant Date Fair Value (in dollars per share)
Outstanding as of January 1, 2017		22,750			21.69
Granted		170,859			29.05
Vested		(22,750	)		21.69
Forfeited		(16,400	)		29.05
RSUs Outstanding at December 31, 2017		154,459		$	29.05

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

Share-based compensation expense for the years ended December 31, 2017, 2016 and 2015 is classified in the consolidated statements of operations as follows:

	For the Year Ended December 31,
	2017		2016		2015
	(in thousands)
Research and development expenses	$	7,670	$	4,936	$	2,268
General and administrative expenses		4,473		1,911		1,756
Total share-based compensation expense	$	12,143	$	6,847	$	4,024

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,
	2017	2016	2015
Risk-free interest rate	1.49% – 2.23%	1.15% – 2.18%	1.56% - 1.89%
Expected term (in years)	3.00 – 6.25	3.00 – 6.25	5.52 - 6.12
Expected volatility	68.95% – 72.24%	60.89% – 68.76%	62.14% - 71.02%
Expected dividend yield	0%	0%	0%

Non-Employees 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 non-employees during the period were as follows:

		Year Ended December 31, 2015
Risk-free interest rate		2.06% - 2.35%
Expected term (in years)		9.19 - 10.00
Expected volatility		62.65% - 69.80%
Expected dividend yield		0%