Stock Options (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Schedule of stock option activity

A summary of the activity under the Plan is as follows:

	Number of Shares	Weighted- Average Exercise Price		Weighted Average Remaining Contractual Term	Aggregate Intrinsic Value
Outstanding at January 1, 2020	4,720,772	$	5.24	7.3	$	9,836
Granted	2,359,074	11.96
Exercised	(697,428)	4.50
Cancelled	(269,470)	7.05
Outstanding at December 31, 2020	6,112,948	$	7.84	7.3	$	114,729
Exercisable at December 31, 2020	3,147,379	$	5.14	6.1	$	67,562

Schedule of restricted stock unit activity

A summary of the RSU activity under the 2017 Plan is as follow:

	Number of Shares	Weighted-Average Remaining Contractual Term	Aggregate Intrinsic Value		Weighted-Average Grant Date Fair Value
Unvested at January 1, 2020	447,336	1.5	$	2,564	$	4.00
Granted	361,932	—			8.14
Vested	—	—			—
Forfeited	(92,501)	—			4.68
Unvested at December 31, 2020	716,767	1.0	$	19,073	$	6.00

Schedule of stock-based compensation expense by award type

The following table presents stock-based compensation expense by award type included within the Company’s consolidated statement of operations and comprehensive loss:

	Year ended December 31,
	2020		2019		2018
Stock options	$	5,725	$	4,230	$	3,754
Restricted stock units	1,187		410		—
Employee stock purchase plan	260		232		130
Stock-based compensation expense included in Total operating expenses	$	7,172	$	4,872	$	3,884

Schedule of stock-based compensation expense as reflected in the Company’s condensed consolidated statements of operations and comprehensive loss

The following table presents stock-based compensation expense as reflected in the Company’s consolidated statements of operations and comprehensive loss:

	Year ended December 31,
	2020		2019		2018
Research and development	$	3,841	$	2,245	$	1,788
General and administrative	3,331		2,627		2,096
Stock-based compensation expense included in Total operating expenses	$	7,172	$	4,872	$	3,884

Schedule of weighted average assumptions for estimating fair value of option awards

The fair value of each option award is estimated on the date of grant using the Black–Scholes option pricing model with the following weighted average assumptions:

	December 31,
	2020		2019		2018
Risk-free interest rate	1.2	%	2.3	%	2.7	%
Expected dividend yield	—	%	—	%	—	%
Expected term (years)	6.05		5.99		6.07
Expected stock price volatility	74	%	74	%	73	%