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Stock-based compensation (Tables)
 9 Months Ended
Sep. 30, 2022
Share-Based Payment Arrangement [Abstract]  
Schedule of Stock Option Activity Under Plan A summary of stock option activity is as follows:
Number
of Shares		Weighted-
Average
Exercise Price
Outstanding at January 1, 20228,342,429 $11.25 
Granted2,765,034 5.41 
Exercised(54,299)3.81 
Cancelled(528,384)13.33 
Outstanding at September 30, 202210,524,780 $9.65 
Vested and expected to vest at September 30, 202210,524,780 $9.65 
Exercisable at September 30, 20225,339,351 $8.96 
Schedule of Restricted Stock Activity A summary of the RSU activity is as follows:
Number of Shares
Unvested at January 1, 2022817,609 
Granted1,379,849 
Vested(190,841)
Forfeited(135,935)
Unvested at September 30, 20221,870,682 
Schedule of Stock-Based Compensation Expense by Award Type The following table presents stock-based compensation expense by award type included within the Company’s condensed consolidated statements of operations and comprehensive loss:
Three Months Ended September 30,Nine Months Ended September 30,
(in thousands)2022202120222021
Stock options$3,901 $3,986 $11,952 $10,617 
Restricted stock units1,365 881 3,832 2,636 
Employee stock purchase plan109 61 424 296 
Stock-based compensation expense included in total operating expenses$5,375 $4,928 $16,208 $13,549 
Schedule of Stock-Based Compensation Expense as Reflected in the Company's Condensed Consolidated Statements of Operations and Comprehensive Loss The following table presents stock-based compensation expense as reflected in the Company’s condensed consolidated statements of operations and comprehensive loss:
Three Months Ended September 30,Nine Months Ended September 30,
(in thousands)2022202120222021
Research and development$2,890 $2,607 $8,569 $7,410 
General and administrative2,485 2,321 7,639 6,139 
Stock-based compensation expense included in total operating expenses$5,375 $4,928 $16,208 $13,549 
Schedule of Weighted Average Assumptions for Estimating Fair Value of Option Awards The fair value of each option award is estimated on the date of grant using the Black-Scholes option pricing model with the following weighted average assumptions:
Three Months Ended
September 30,		Nine Months Ended September 30,
2022202120222021
Risk-free interest rate2.9 %1.0 %2.0 %0.8 %
Expected dividend yield— %— %— %— %
Expected term (years)6.116.115.996.05
Expected stock price volatility94 %82 %88 %83 %