Stock-Based Awards (Tables)

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Summary of Stock Option Activity

The following table summarizes option award activity under the 2017 Plan and the 2015 Plan: 

	Number of Options	Weighted- Average Exercise Price		Weighted- Average remaining contractual life (years)	Aggregate Intrinsic Value (in thousands)
Balance at December 31, 2021	13,686,386	$	24.33	6.76	$	333,011
Granted	2,255,840	43.06
Exercised	(720,904)	14.59
Forfeited	(547,605)	41.82
Balance at December 31, 2022	14,673,717	$	27.03	6.24	$	127,865
Vested and expected to vest at December 31, 2022	13,083,022	$	30.24	6.67	$	84,709
Exercisable at December 31, 2022	9,886,659	$	21.71	5.66	$	101,574

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

The following assumptions were used in estimating the fair value of grants during the:

	Year Ended December 31,
	2022	2021	2020
Expected term (in years)	5.50 - 6.08	5.50 - 6.08	5.50 - 6.08
Volatility	65.1% - 66.3%	61.0% - 63.4%	65.2% - 67.1%
Risk-free interest rate	1.5% - 4.3%	0.5% - 1.3%	0.3% - 1.7%
Dividend yield	—	—	—

Summary of Restricted Stock Activity

Aggregated information regarding RSUs granted under the Plan for the year ended December 31, 2022 is summarized below:

	Number of Units	Weighted-Average Fair Value at Date of Grant per Share
Unvested at December 31, 2021	2,629,980	$	43.97
Granted	1,797,231	37.55
Vested and released	(837,096)	40.30
Forfeited	(259,461)	44.52
Unvested and expected to vest at December 31, 2022	3,330,654	$	41.39

Summary of Stock-Based Compensation Expense

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

	Year Ended December 31,
	2022		2021		2020
Research and development	$	60,196	$	50,036	$	29,002
General and administrative	39,651		35,211		21,349
Total	$	99,847	$	85,247	$	50,351