Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2020

Stock-Based Compensation

Summary of stock option activity

	Options Outstanding and Exercisable
				Weighted
		Weighted		Average	Aggregate
		Average		Remaining	Intrinsic
	Number of	Exercise		Contractual	Value(1)
	Shares	Price		Life (Years)	(in thousands)
Outstanding as of December 31, 2019	2,170,212	$	6.51	8.6	$	113,295
Granted	884,525	$	41.65	9.9		—
Exercised	(17,142)	$	2.08	7.5		—
Forfeitures	(22,000)	$	15.57	9.2		—
Outstanding as of March 31, 2020	3,015,595	$	16.77	9.0	$	65,322
Vested and expected to vest as of March 31, 2020	3,015,595	$	16.77	—	$	65,322
Exercisable as of March 31, 2020	828,250	$	3.97	—	$	27,417

The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money at March 31, 2020 and December 31, 2019.

Summary of stock based compensation expense recorded

	Three Months Ended
	March 31,
(in thousands)	2020		2019
Research and development	$	452	$	149
General and administrative		556		234
Total stock-based compensation expense	$	1,008	$	383

Summary of assumptions used in the Black Scholes option pricing model for stock options granted

	Three Months Ended
	March 31,
	2020		2019
Expected term	6.08	years	—	years
Expected volatility	69.7	%	—	%
Risk free interest rate	0.6 - 1.0	%	—	%
Expected dividend yield	—	%	—	%