Stock-Based Awards (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Summary of Stock Option Plans Activity

Activity under the Company’s stock option plans is set forth below:

	Number of Options	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term	Aggregate Intrinsic Value
				(Years)	(in thousands)
Outstanding at December 31, 2022	10,604,367	$	31.70	7.6
Granted	3,296,741	$	23.70
Exercised	(487,014)	$	7.15
Forfeited	(2,061,875)	$	31.47
Outstanding at December 31, 2023	11,352,219	$	30.47	7.1	$	8,141
Vested and expected to vest at December 31, 2023	11,352,219	$	30.47	7.1	$	8,141
Vested and exercisable at December 31, 2023	6,582,670	$	31.26	6.2	$	8,098

Summary of Assumptions Used for Estimating the Fair Value of Stock Options Granted

The fair value of stock options granted to employees was estimated on the date of grant using the Black-Scholes option-pricing model with the following assumptions:

	Years Ended December 31,
	2023	2022	2021
Expected term of options (in years)	5.5 – 6.1	5.3 – 6.1	5.3 – 6.1
Expected stock price volatility	99.0% – 101.5%	101.4% – 111.2%	103.1% – 112.1%
Risk-free interest rate	3.4% – 4.9%	1.6% – 4.3%	0.6% – 1.3%
Expected dividend yield	—	—	—

Summary of Employees Stock Purchase Plan

The fair value of employees’ purchase rights under the ESPP was estimated on the date of grant using the Black-Scholes option-pricing model with the following assumptions:

	Years Ended December 31,
	2023	2022	2021
Expected term of ESPP (in years)	0.5	0.5	0.5
Expected stock price volatility	41.2% - 95.1%	59.0% - 86.0%	76.1% - 144.1%
Risk-free interest rate	4.5% - 5.2%	0.10% - 4.5%	0.04% - 0.1%
Expected dividend yield	—	—	—

Summary of Restricted Stock Activity

The Company’s RSUs activity was summarized as follows:

	Shares	Weighted Average Grant Date Fair Value Per Share
Unvested as of December 31, 2022	2,667,828	$	37.46
Granted	3,534,242	$	24.91
Vested	(734,662)	$	38.91
Forfeited	(662,441)	$	33.45
Unvested as of December 31, 2023	4,804,967	$	28.56

Summary of Stock-based Compensation Expense

The following table sets forth the total stock-based compensation expense for all awards granted to employees and the ESPP in the consolidated statements of operations (in thousands):

	Years Ended December 31,
	2023		2022		2021
Research and development	$	62,745	$	53,153	$	42,554
Selling, general and administrative	48,571		48,929		41,230
Total stock-based compensation	$	111,316	$	102,082	$	83,784