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Stock-based Compensation (Tables)
 12 Months Ended
Dec. 31, 2021
Share-based Payment Arrangement [Abstract]  
Schedule of Stock-based Compensation Expense
Stock-based compensation expense is included in the consolidated statements of operations as follows (in thousands): 
 Year Ended December 31,
 202120202019
Research and development$2,353 $1,620 $1,562 
Selling, general and administrative9,240 6,108 5,381 
Total$11,593 $7,728 $6,943 
The following table presents total stock-based compensation expense by security type included in the consolidated statements of operations (in thousands):
 Year Ended December 31,
 202120202019
Stock options$2,764 $2,381 $2,149 
RSUs and RSAs2,768 2,2311,805
PSUs2,333 1,160 1,087 
PBOs3,728 1,9561,902
Total$11,593 $7,728 $6,943 
Assumptions Used to Estimate the Fair Value of Option Grants The following summarizes the weighted-average assumptions used to estimate the fair value of employee and non-employee stock options granted:
 Year Ended December 31,
 202120202019
Expected life (years)5.65.35.6
Volatility52.5 %50.4 %55.3 %
Risk-free interest rate0.8 %1.0 %2.4 %
Expected dividend yield0.0 %0.0 %0.0 %
The following summarizes the weighted-average assumptions used to estimate the fair value of 9,000 and 76,000 shares of stock options granted to non-employees for services valued at $0.1 million and $0.4 million during the years ended December 31, 2021 and 2020 respectively:
 Year Ended December 31,
 20212020
Expected life (years)5.65.4
Volatility54.1 %51.6 %
Risk-free interest rate0.9 %0.4 %
Expected dividend yield0.0 %0.0 %
Schedule of Share-based Compensation, Stock Options, Activity
The following tables summarizes stock option activities:
Number
of
Shares		Weighted
Average
Exercise Price Per Share
(In Thousands)
Outstanding at December 31, 20184,112 $4.81 
Granted406 $20.68 
Exercised(1,045)$4.50 
Forfeited/Expired(326)$11.01 
Outstanding at December 31, 20193,147 $6.31 
Granted496 $13.30 
Exercised(210)$6.30 
Forfeited/Expired(48)$16.71 
Outstanding at December 31, 20203,385 $7.19 
Granted286 $26.85 
Exercised(664) $6.96 
Forfeited/Expired(72)$17.99 
Outstanding at December 31, 20212,935 $8.90 

Number
of
Shares		Weighted
Average
Exercise Price Per Share		Weighted
Average
Remaining
Contractual Term		Aggregate Intrinsic
Value
(In Thousands)(In Years)(In Thousands)
Outstanding at December 31, 20212,935 $8.90 5.0$65,963 
Exercisable at December 31, 20212,861 $8.56 4.9$65,186 
Vested and expected to vest at December 31, 20212,338 $5.99 4.2$59,103 
Schedule of Share-based Compensation, RSA Activity The following table summarizes RSA activities:
Number
of
Shares		Weighted Average
Grant Date
Fair Value
Per Share
(In Thousands)
Non-vested balance at December 31, 201855 $12.83 
Granted40 $17.18 
Vested(56)$12.83 
Forfeited/Expired(4)$17.18 
Non-vested balance at December 31, 201935 $17.18 
Granted96 $11.44 
Vested(35)$17.18 
Non-vested balance at December 31, 202096 $11.44 
Granted46 $21.91 
Vested(62)$11.31 
Non-vested balance at December 31, 202180 $17.53 
Schedule of Share-based Compensation, RSU Activity The following table summarizes RSU activities:
Number
of
Shares		Weighted Average
Grant Date
Fair Value
Per Share
(In Thousands)
Non-vested balance at December 31, 2018348 $5.66 
Granted72 $19.19 
Vested(210)$5.03 
Forfeited/Expired(9)$13.60 
Non-vested balance at December 31, 2019201 $10.76 
Granted156 $14.22 
Vested(168)$10.05 
Forfeited/Expired(13)$15.16 
Non-vested balance at December 31, 2020176  $14.17 
Granted163 $26.59 
Vested(70)$13.57 
Forfeited/Expired(37)$21.89 
Non-vested balance at December 31, 2021232 $21.83 
Share-based Compensation, Performance Shares Award Outstanding Activity The following table summarizes PSU activities:
Number
of
Shares		Weighted Average
Grant Date
Fair Value
Per Share
(In Thousands)
Non-vested balance at December 31, 2018240 $7.48 
Granted95 $14.98 
Vested(200)$6.58 
Forfeited/Expired(15)$15.58 
Non-vested balance at December 31, 2019120 $13.88 
Granted124 $13.59 
Vested(107)$11.28 
Forfeited/Expired(6)$21.80 
Non-vested balance at December 31, 2020131  $15.34 
Granted82 $26.16 
Vested(66)$16.14 
Forfeited/Expired(19)$19.38 
Non-vested balance at December 31, 2021128 $21.24 
The following tables summarizes PBO activities:
Number
of
Shares		Weighted Average Grant Date Fair Value Per Share
(In Thousands)
Outstanding at December 31, 20181,582 $3.47 
Granted718 $11.44 
Exercised(422)$3.17 
Forfeited/Expired(618)$10.34 
Outstanding at December 31, 20191,260 $4.75 
Granted689 $6.37 
Forfeited/Expired(389)$6.42 
Outstanding at December 31, 20201,560 $5.05 
Granted433 $12.23 
Exercised(35)$9.02 
Forfeited/Expired(118)$12.23 
Outstanding at December 31, 20211,840 $4.11 

Number
of
Shares		Weighted
Average
Exercise Price Per Share		Weighted
Average
Remaining
Contractual Term		Aggregate Intrinsic
Value
(In Thousands)(In Years)(In Thousands)
Exercisable at December 31, 20211,374 $9.08 6.0$30,809 
Vested and expected to vest at December 31, 20211,784 $12.11 6.6$34,263 
Schedule of Assumptions Used The following summarize the ranges of weighted-average assumptions used to estimate the fair value of employee stock options granted:
 Year Ended December 31,
202120202019
Expected life (years)5.55.35.6
Volatility51.9 %49.9 %55.8 %
Risk-free interest rate0.7 %1.3 %2.5 %
Expected dividend yield0.0 %0.0 %0.0 %