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Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2021
Share-based Payment Arrangement [Abstract]  
Summary of Assumptions used to Determine the Fair Value of Options Granted to Employees and Directors The assumptions that the Company used to determine the fair value of options granted to employees and directors were as follows, presented on a weighted average basis:
Year Ended December 31,
202120202019
Risk-free interest rate1.0 %1.2 %2.2 %
Expected term (in years)5.86.16.2
Expected volatility77.8 %77.2 %74.5 %
Expected dividend yield0 %0 %0 %
Summary of Option Activity The following table summarizes the Company's option activity from January 1, 2021 to December 31, 2021:
Number of SharesWeighted Average Exercise PriceWeighted Average Remaining Contractual Term
(in years)		Aggregate Intrinsic Value
(in thousands)
Outstanding as of December 31, 20205,712,339 $29.53 
Granted2,877,170 $26.80 
Exercised(577,605)$8.17 
Forfeited/Expired(572,396)$40.49 
Outstanding as of December 31, 20217,439,508 $29.28 7.86$3,891 
Options vested and expected to vest as of December 31, 20217,439,508 $29.28 7.86$3,891 
Options exercisable as of December 31, 20213,599,498 $29.06 6.65$3,103 
Summary of RSU Activity The table below summarizes the Company's time-based restricted stock unit activity from January 1, 2021 to December 31, 2021:
Number
of Shares		Weighted
Average
Grant Date
Fair Value
Unvested at December 31, 2020438,625 $49.28 
Granted1,341,899 $31.12 
Vested(112,854)$48.48 
Forfeited(129,938)$46.95 
Unvested at December 31, 20211,537,732 $33.68 
Classification of Stock-Based Compensation Expense
Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows:
 Year Ended December 31,
(in thousands)202120202019
Research and development$20,698 $17,443 $7,934 
Selling, general, and administrative25,380 19,694 12,476 
Total stock-based compensation$46,078 $37,137 $20,410 
The following table summarizes share-based compensation expense associated with each of our share-based compensation arrangements:
Year Ended December 31,
(in thousands)202120202019
Stock options$36,263 $29,925 $19,328 
Time-based restricted stock units9,047 4,424 1,082 
Performance-based restricted stock units— 1,907 — 
Employee stock purchase plan768 881 — 
Total stock-based compensation expense$46,078 $37,137 $20,410