Share-based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Assumptions Used to Estimate Fair Values of Share Options Granted

The following table presents the assumptions used to estimate the fair values of the share options granted in the years presented:

	March 2016			August 2016			December 2016			May 2017			September 2017			2018
Risk-free rate    of return		2.8	%		2.5	%		3.4	%		3.2	%		3.5	%	2.7%-3.2%
Contractual life    of option	10 years			10 years			10 years			10 years			10 years			10 years
Expected    term	n/a			n/a			n/a			n/a			n/a			6.5 years
Estimated    volatility rate		70	%		70	%		70	%		70	%		70	%		70	%
Expected    dividend    yield		0	%		0	%		0	%		0	%		0	%		0	%
Fair value of    underlying    ordinary    shares		7.14			8.04			8.04			9.60			27.93		17.60-24.58

Summary of Option Activity

A summary of option activity under the Plan during the years ended December 31, 2016, 2017 and 2018 is presented below:

	Number of options			Weighted average exercise price		Weighted average remaining contractual term		Aggregate intrinsic value
				$		Years		$
Outstanding at January 1, 2016		4,309,232			0.60		9.68		18,874,438
Granted		2,918,993			1.53		—		—
Forfeited		(84	)		1.74		—		—
Outstanding at December 31, 2016		7,228,141			0.97		9.00		53,677,170
Granted		264,480			8.76		—		—
Exercised		(100,834	)		0.65		—		—
Forfeited		(843,410	)		1.11		—		—
Outstanding at December 31, 2017		6,548,377			1.28		8.06		130,668,851
Granted		2,759,750			21.15		—		—
Exercised		(256,065	)		0.76		—		—
Forfeited		(290,327	)		3.73		—		—
Outstanding at December 31, 2018		8,761,735			7.47		7.80		138,009,758
Vested and Exercisable as of     December 31, 2018		3,321,376			1.01		6.93		73,775,871
Vested or expected to vest as of     December 31, 2018		8,761,735			7.47		7.80		138,009,758

Allocation of Compensation Expense Related to Option

The weighted-average grant-date fair value of the options granted in 2016, 2017 and 2018 were $6.94, $13.92 and $14.03 per share, respectively. The Group recorded compensation expense related to the options of $3,524,733, $4,751,933 and $9,403,059 for the year ended December 31, 2016, 2017 and 2018, respectively, which were classified in the accompanying consolidated statements of operations as follows:

	Year ended December 31,
	2016		2017		2018
	$		$		$
Selling, general and administrative		1,472,993		2,215,282		4,428,266
Research and development		2,051,740		2,536,651		4,974,793
Total		3,524,733		4,751,933		9,403,059

Allocation of Compensation Expense Related to Restricted Shares

As of December 31, 2018, there was $14,386,103 of total unrecognized compensation expense related to non-vested restricted shares. The Group recorded compensation expense related to the restricted shares of $1,400,545, $5,179,173 and $2,826,584 for the year ended December 31, 2016, 2017 and 2018, respectively, which were classified in the accompanying consolidated statements of operations as follows:

	Year ended December 31,
	2016		2017		2018
	$		$		$
Selling, general and administrative		825,822		3,848,165		2,206,046
Research and development		574,723		1,331,008		620,538
Total		1,400,545		5,179,173		2,826,584