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Stock-based compensation (Tables)
 9 Months Ended
Sep. 30, 2021
Share-based Payment Arrangement [Abstract]  
Schedule of stock based compensation expense
The following table summarizes the stock-based compensation expense recognized in the three and nine months ended September 30, 2021 and 2020 (in thousands):
 Three Months Ended
September 30,		Nine Months Ended
September 30,
 2021202020212020
Cost of goods sold$403 $607 $1,523 $1,765 
Research and development565 748 2,171 2,505 
Sales and marketing353 565 1,168 1,833 
General and administrative873 853 2,949 2,975 
 $2,194 $2,773 $7,811 $9,078 
Schedule of stock option and restricted stock unit activity
The following table summarizes the Company’s stock option and RSU activity, excluding market and performance-based RSUs, during the three and nine months ended September 30, 2021: 
Stock OptionsRestricted Stock Units
 Number of
Shares		Number of
Units
Balance as of December 31, 20202,096,917 3,621,681 
Granted
60,944 1,434,500 
Exercised/Converted
(529,482)(1,445,813)
Cancelled/Forfeited
(24,393)(336,294)
Balances at September 30, 20211,603,986 3,274,074 
Schedule of estimated fair value of certain stock-based awards using Black-Scholes-Merton valuation model The fair value of market-based RSUs was measured on the grant date using Monte Carlo simulation model with the following assumptions:
Assumptions
Used
Weighted-average volatility66%
Risk-free interest rate2.79%
Expected dividends—%