Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Share-based Payment Arrangement [Abstract]

Summary of stock option activity

The following table summarizes stock option activity during the twelve months ended December 31, 2021:

	Shares			Weighted average exercise price		Weighted average remaining contractual life (years)		Aggregate intrinsic value (in thousands)
Outstanding at January 1, 2021		1,837,540		$	71.80
Options granted		687,059			109.03
Options exercised		(11,080	)		92.96
Options cancelled		(211,945	)		114.34
Outstanding at December 31, 2021		2,301,574		$	78.89		6.51	$	62,566
Exercisable at December 31, 2021		1,432,144		$	62.66		5.38	$	60,932

Schedule of stock-based compensation expense

Stock-based compensation expense during the years ended December 31, 2021, 2020 and 2019 was as follows (in thousands):

	Years Ended December 31,
	2021		2020		2019
Stock-based compensation expense by type of award:
Stock options	$	26,873	$	20,730	$	22,487
Restricted stock		—		—		272
Total stock-based compensation expense	$	26,873	$	20,730	$	22,759
Effect of stock-based compensation expense by line item:
Research and development	$	10,698	$	8,833	$	8,277
General and administrative		16,175		11,897		14,482
Total stock-based compensation expense included in net loss	$	26,873	$	20,730	$	22,759