Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2023

Stock-Based Compensation Expense by Award Type

The Company’s stock-based compensation expense by award type was as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2023		2022		2023		2022
Stock options	$	7,416	$	8,825	$	15,594	$	18,092
Restricted stock units		2,852		1,258		5,632		2,511
Employee stock purchase plan		236		252		484		532
	$	10,504	$	10,335	$	21,710	$	21,135

Stock-Based Compensation Expense

The Company recorded aggregate stock-based compensation expense in the consolidated statements of operations and comprehensive loss as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2023		2022		2023		2022
Research and development	$	5,470	$	5,405	$	11,540	$	11,075
General and administrative		5,034		4,930		10,170		10,060
	$	10,504	$	10,335	$	21,710	$	21,135

Summary of Unvested RSUs Activity Under 2015 Plan

The following table summarizes restricted stock unit activity under the 2015 Plan (in thousands, except per share data):

				Weighted-average
				Grant Date
	Shares			Fair Value
Unvested balance at December 31, 2022		613		$	35.41
Granted		1,005		$	22.14
Vested		(146	)	$	36.31
Forfeited		(48	)	$	27.37
Unvested balance at June 30, 2023		1,424		$	26.22

2014 and 2015 Equity Incentive Plan [Member]

Summary of Stock Option Activity

The following table summarizes stock option activity under the 2014 Plan and 2015 Plan (in thousands, except per share data):

						Weighted-
						average
				Weighted-		Remaining
				average		Contractual		Aggregate
				Exercise		Life		Intrinsic
	Shares			Price		(Years)		Value (a)
Outstanding at December 31, 2022		7,668		$	34.43		6.5	$	15,783
Granted		1,661		$	21.99
Exercised		(165	)	$	7.40
Cancelled or forfeited		(259	)	$	36.73
Outstanding at June 30, 2023		8,905		$	32.54		6.7	$	9,867
Exercisable at June 30, 2023		5,781		$	34.41		5.5	$	9,798
Vested and expected to vest at June 30, 2023		8,905		$	32.54		6.7	$	9,867

(a) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the fair value of the common stock for the options that were in the money at the dates reported.