Stock-Based Awards (Tables)

12 Months Ended

Dec. 31, 2022

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, 2021		10,308,928		$	31.75		8.2
Granted		2,051,535		$	28.07
Exercised		(696,963	)	$	6.51
Forfeited		(1,059,133	)	$	41.67
Outstanding at December 31, 2022		10,604,367		$	31.70		7.6	$	52,307
Vested and expected to vest at December 31, 2022		10,604,367		$	31.70		7.6	$	52,307
Vested and exercisable at December 31, 2022		6,069,564		$	27.06		7.0	$	48,178

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:

	Year Ended December 31,
	2022	2021	2020
Expected term of options (in years)	5.3 – 6.1	5.3 – 6.1	5.0 – 6.1
Expected stock price volatility	101.4% – 111.2%	103.1% – 112.1%	88.8% – 108.6%
Risk-free interest rate	1.6% – 4.3%	0.6% – 1.3%	0.3% – 1.2%
Expected dividend yield	—	—	—

Summary of Restricted Stock Activity

The Company’s RSAs and RSUs were summarized as follows:

	Shares			Weighted Average Grant Date Fair Value Per Share
	RSU			RSU
Unvested as of December 31, 2021		1,271,334		$	59.93
Granted		2,097,128		$	27.87
Vested		(349,496	)	$	58.26
Forfeited		(349,788	)	$	40.86
Unvested as of December 31, 2022		2,669,178		$	37.46

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:

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

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:

	Year Ended December 31,
	2022		2021		2020
	(in thousands)
Research and development	$	53,153	$	42,554	$	13,663
Selling, general and administrative	$	48,929	$	41,230		13,937
Total stock-based compensation	$	102,082	$	83,784	$	27,600