Share-Based Payments (Tables)

12 Months Ended

Dec. 31, 2017

SOP 2007

Share-Based Payments

Schedule of movements in the number of share options outstanding and their related weighted average exercise prices

	2015					2016					2017
Stock Option Plan 2007	Weighted average exercise price in $ per share		Options			Weighted average exercise price in $ per share		Options			Weighted average exercise price in $ per share		Options			Aggregate intrinsic value
Outstanding as of January 1		0.73		241,330			0.73		234,760			0.73		109,960
Granted		—		—			—		—			—		—
Exercised		0.73		(6,570	)		0.73		(124,540	)		0.73		(108,440	)
Forfeited		—		—			0.73		(260	)		0.73		(1,520	)
Outstanding as of December 31		0.73		234,760			0.73		109,960			—		—		$	—
Vested and exercisable as of December 31		0.73		229,270			0.73		107,900			—		—		$	—

SOP 2015

Share-Based Payments

Schedule of movements in the number of share options outstanding and their related weighted average exercise prices

	2015					2016					2017
Stock Option Plan 2015	Weighted average exercise price in $ per share		Options			Weighted average exercise price in $ per share		Options			Weighted average exercise price in $ per share		Options			Aggregate intrinsic value
Outstanding as of January 1		—		—			7.61		1,092,300			7.83		1,794,360
Granted		7.61		1,093,550			8.02		922,130			9.02		1,458,300
Exercised		—		—			7.21		(23,360	)		—		—
Forfeited		7.21		(1,250	)		7.64		(196,710	)		8.60		(207,761	)
Outstanding as of December 31		7.61		1,092,300			7.83		1,794,360			8.35		3,044,899		$	9
Vested and exercisable as of December 31		7.21		86,620			7.52		425,210			7.68		989,656		$	3

Summary of assumptions used for valuation of options

Input parameters	2015	2016	2017
Expected volatility	55.0% - 70.0%	59.8% - 67.2%	55.6% - 62.0%
Expected term of options	2.0 years	6.0 years	6.1 years
Risk-free interest rate	(0.40)% - (0.21)%	1.15% - 2.09%	1.89% - 2.10%
Expected dividend yield	—	—	—

2017 Plan

Share-Based Payments

Schedule of movements in the number of share options outstanding and their related weighted average exercise prices

	2017
2017 Plan	Weighted average exercise price in $ per share		Options		Aggregate intrinsic value
Outstanding as of January 1, 2017		—		—
Granted		6.92		294,100
Exercised		—		—
Forfeited		—		—
Outstanding as of December 31, 2017		6.92		294,100	$	—
Vested and exercisable as of December 31, 2017		—		—	$	—

Summary of assumptions used for valuation of options

Input parameters
Range of expected volatility	59.5% - 63.0%
Expected term of options (in years)	6.0
Range of risk-free interest rate	1.93% - 2.27%
Dividend yield	—

Schedule of allocation of share-based compensation expense

	December 31,
(in thousands)	2015		2016		2017
Research and development	$	418	$	894	$	2,128
General and administrative		933		1,651		3,604
Total	$	1,351	$	2,545	$	5,732