STOCK-BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation Expense

The following table shows total stock-based compensation expense recognized in the accompanying Consolidated Statements of Operations (in thousands):

	Year Ended December 31,
	2022		2021		2020
Research and development	$	18,404	$	19,534	$	13,523
General and administrative	13,246		13,422		12,185
Total stock-based compensation expense	$	31,650	$	32,956	$	25,708

Assumptions Used for Estimating Fair Value of Employee Stock Options

The assumptions used for estimating the fair value of the employee stock options were as follows:

	Year Ended December 31,
	2022	2021	2020
Risk-free interest rate	2.15-3.69%	0.95-1.22%	0.34-0.61%
Expected term (in years)	5.46-5.49	5.46-5.52	5.51-5.57
Expected dividend yield of stock	—	—	—
Expected volatility	72.38-76.01%	77.30-79.77%	77.61-80.32%

Weighted-Average Assumptions Used for Estimating Fair Value of ESPP Purchase Rights

The assumptions used for estimating the fair value of the ESPP purchase rights are as follows:

	Year Ended December 31,
	2022	2021	2020
Risk-free interest rate	1.62-4.61%	0.01-2.80%	1.53-2.80%
Expected term (in years)	0.5-2.0	0.0-2.0	0.5-2.0
Expected dividend yield of stock	—	—	—
Expected volatility	57.97-72.14%	32.54-97.88%	51.02-91.96%