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Stock-based compensation (Tables)
 6 Months Ended
Jun. 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 six months ended June 30, 2021 and 2020 (in thousands):
 Three Months Ended
June 30,		Six Months Ended
June 30,
 2021202020212020
Cost of goods sold$572 $621 $1,120 $1,158 
Research and development744 999 1,606 1,757 
Sales and marketing261 738 815 1,268 
General and administrative763 1,429 2,076 2,122 
 $2,340 $3,787 $5,617 $6,305 
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 six months ended June 30, 2021: 
Stock OptionsRestricted Stock Units
 Number of
Shares		Number of
Units
Balance as of December 31, 20202,096,917 3,621,681 
Granted
53,487 89,744 
Exercised/Converted
(398,627)(999,459)
Cancelled/Forfeited
(17,393)(246,851)
Balances at June 30, 20211,734,384 2,465,115 
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—%