Stock-Based Compensation

6 Months Ended

Jun. 30, 2022

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

4. Stock-Based Compensation

The following table summarizes the total stock-based compensation expense included in the Company’s statements of operations for the periods presented (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
Cost of product sales	$	346	$	423	$	669	$	586
Research and development		7,232		7,319		12,696		12,149
Selling, general and administrative		12,934		14,263		22,110		22,454
	$	20,512	$	22,005	$	35,475	$	35,189

The fair value of each employee stock option and each employee stock purchase plan right granted is estimated on the grant date under the fair value method using the Black-Scholes valuation model, which requires the Company to make a number of assumptions including the estimated expected life of the award and related volatility. The fair value of restricted stock units is estimated based on the market price of the Company’s common stock on the date of grant. The estimated fair values of stock options, purchase plan rights, and restricted stock units are then expensed over the requisite service period, which is generally the vesting period. For restricted stock units requiring satisfaction of both market and service conditions, the estimated fair values are generally expensed over the longest of the explicit, implicit and derived service periods. Performance-based stock awards vest upon the achievement of certain pre-defined company-specific performance-based criteria. Expense related to these performance-based stock awards is generally recognized ratably over the expected performance period once the pre-defined performance-based criteria for vesting becomes probable.