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Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]  
Schedule of non-cash stock-based compensation expense
Non-cash stock-based compensation expense (service-based stock options, restricted stock units and employee stock purchase plan) is summarized in the following table: 
 Years Ended December 31,
(in thousands)202320222021
Cost of product sales$2,970 $3,630 $3,681 
Research and development3,705 5,261 4,120 
Selling, general and administrative25,650 28,292 26,521 
Total non-cash stock-based compensation expense$32,325 $37,183 $34,322 
Schedule of fair value assumptions
The fair value of each service-based stock option grant for the reported periods is estimated on the date of the grant using the Black-Scholes option-pricing model using the assumptions noted in the following table:
 Year Ended December 31,
Service-Based Stock Options202320222021
Expected dividend rate—%—%—%
Expected stock price volatility
62.5 - 66.7%
63.8 - 75.3%
71.5 - 76.7%
Risk-free interest rate
3.4 - 4.7%
1.5 - 4.4%
0.53 -1.5%
Expected life (years)5.5
5.3 - 6.3
5.3 - 6.3
Weighted-average grant date fair value$18.85$19.83$32.96
Summary of activity for service-based stock options
The following table summarizes the activity for service-based stock options for the indicated periods: 
Service-Based Stock OptionsOptions
Weighted-Average
 Exercise Price
Weighted-Average
 Remaining
 Contractual Term
(Years)
Aggregate
 Intrinsic
 Value
(Thousands)
Outstanding at December 31, 20226,609,147 $24.89 6.8$56,708 
Granted607,947 30.90 
Exercised(377,597)12.55 
Expired(41,004)45.21 
Forfeited(81,807)37.96 
Outstanding at December 31, 20236,716,686 $25.85 6.16$88,387 
Exercisable at December 31, 20234,967,797 $22.16 5.45$82,288 
Summary of activity for restricted stock awards
The following table summarizes the activity for restricted stock units for the indicated periods: 
Restricted Stock UnitsNumber of Restricted Stock UnitsWeighted-Average Grant Date Fair Value
Outstanding at December 31, 2022648,174 $34.86 
Granted564,449 30.36 
Vested(224,142)32.34 
Forfeited(57,545)33.01 
Unvested at December 31, 2023930,936 $32.85