Stock-based compensation (Tables)

3 Months Ended

Mar. 31, 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 months ended March 31, 2021 and 2020 (in thousands):

	Three Months Ended March 31,
	2021		2020
Cost of goods sold	$	548	$	537
Research and development	862		758
Sales and marketing	554		530
General and administrative	1,313		693
	$	3,277	$	2,518

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 months ended March 31, 2021: 

	Stock Options	Restricted Stock Units
	Number of Shares	Number of Units
Balance as of December 31, 2020	2,096,917	3,621,681
Granted	—	6,950
Exercised/Converted	(199,607)	(199,394)
Cancelled/Forfeited	(59)	(63,888)
Balances at March 31, 2021	1,897,251	3,365,349

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 volatility	66%
Risk-free interest rate	2.79%
Expected dividends	—%