Share Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of stock option activity under the Plans

				Weighted
		Weighted		Average
		Average		Remaining	Aggregate
	Number of	Exercise		Contractual	Intrinsic
	Shares	Price		Term	Value
				(in years)
Outstanding as of December 31, 2018	5,960,939	$	10.25	8.56	$	108,352
Granted	3,608,588	$	13.44
Exercised	(150,253)	$	3.93
Forfeited	(927,540)	$	15.26
Outstanding as of December 31, 2019	8,491,734	$	11.17	7.88	$	27,217
Options exercisable as of December 31, 2019	3,373,659	$	7.29	6.24	$	19,903
Options unvested as of December 31, 2019	5,118,075	$	13.74	8.96	$	7,314

Schedule of share-based compensation expense was classified in the consolidated statements of operations and comprehensive loss

	Years Ended
	December 31,
	2019		2018
Research and development expenses	$	5,746	$	2,285
General and administrative expenses		9,334		3,416
	$	15,080	$	5,701

Employees and Directors

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of stock option valuation assumptions presented on weighted average basis

	Years Ended
	December 31,
	2019		2018
Risk-free interest rate	2.07	%	2.82	%
Expected term (in years)	6.22		6.40
Expected volatility	79.14	%	75.04	%
Expected dividend yield	0	%	0	%

Non-employees

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of stock option valuation assumptions presented on weighted average basis

	Years Ended
	December 31,
	2019		2018
Risk-free interest rate	1.38	%	2.91	%
Expected term (in years)	2.77		7.35
Expected volatility	68.17	%	74.18	%
Expected dividend yield	0	%	0	%

Restricted shares

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of restricted share activity

	Class A			Class B
		Weighted			Weighted
		Average			Average
	Number of	Grant Date		Number of	Grant Date
	Shares	Fair Value		Shares	Fair Value
Unvested restricted shares outstanding as of December 31, 2018	133,812	$	0.000273235	743,407	$	0.000273235
Granted	—		—	—		—
Vested	(133,812)	$	0.000273235	(743,407)	$	0.000273235
Unvested restricted shares outstanding as of December 31, 2019	—		—	—		—

Restricted Share Units (RSUs)

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of restricted share activity

		Weighted
		Average
	Number of	Grant Date
	Shares	Fair Value
Unvested RSUs as of December 31, 2018	—	$	—
Granted	328,296	$	12.93
Vested	—	$	—
Forfeited	—	$	—
Unvested RSUs as of December 31, 2019	328,296	$	12.93