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STOCK PLANS
 9 Months Ended
Sep. 30, 2022
Stockholders' Equity Note [Abstract]  
STOCK PLANS STOCK PLANS
Stock-Based Compensation
The Company recognized stock-based compensation expense in the periods presented as follows (in thousands):
Three Months Ended
September 30,		Nine Months Ended
September 30,
2022202120222021
Cost of goods sold$1,599 $1,512 $4,429 $4,429 
Research and development1,783 1,156 4,761 3,591 
Selling, general and administrative9,300 8,116 26,225 23,336 
        Total$12,682 $10,784 $35,415 $31,356 
Stock-based compensation from:
    Stock options$6,711 $6,458 $20,038 $19,507 
    Restricted stock units5,758 4,126 14,588 11,164 
    Employee stock purchase plan213 200 789 685 
        Total$12,682 $10,784 $35,415 $31,356 
Equity Awards
The following tables contain information about the Company’s stock option and restricted stock unit, or RSU, activity for the nine months ended September 30, 2022:
Stock Options Number of Options Weighted Average Exercise Price (Per Share)
 Outstanding at December 31, 2021
6,050,540 $49.32 
     Granted1,034,230 60.16 
     Exercised(667,940)35.18 
     Forfeited(88,766)54.38 
     Expired(24,447)78.76 
 Outstanding at September 30, 2022
6,303,617 52.41 
Restricted Stock Units Number of Units Weighted Average Grant Date Fair Value (Per Share)
Unvested at December 31, 2021
955,277 $52.85 
     Granted598,699 60.43 
     Vested(323,821)50.17 
     Forfeited(68,000)55.04 
Unvested at September 30, 2022
1,162,155 57.38 
The weighted average fair value of stock options granted during the nine months ended September 30, 2022 was $25.66 per share. The fair values of stock options granted were estimated using the Black-Scholes option valuation model with the following weighted average assumptions:
Black-Scholes Weighted Average AssumptionNine Months Ended September 30, 2022
Expected dividend yieldNone
Risk-free interest rate2.84%
Expected volatility45.14%
Expected term of options4.92 years
Employee Stock Purchase Plan
In June 2022, the Company’s stockholders approved the Amended and Restated 2014 Employee Stock Purchase Plan, or ESPP. The ESPP was amended to increase the number of shares of common stock that may be sold under the ESPP by an additional 500,000 shares.
The ESPP features two six-month offering periods per year, running from January 1 to June 30 and July 1 to December 31. Under the ESPP, employees may elect to contribute after-tax earnings to purchase shares at 85% of the closing fair market value of the Company’s common stock on either the offering date or the purchase date, whichever is less. During the nine months ended September 30, 2022, 36,729 shares were purchased and issued through the ESPP.