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Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2020
Share-based Payment Arrangement [Abstract]  
Schedule of Stock Options Activity
The following table summarizes our stock option activity for 2020:
Shares
(in thousands)
Weighted
Average
Exercise
Price
Weighted
Average
Remaining
Contractual
Term (years)
Aggregate
Intrinsic
Value
(in thousands)
Outstanding at December 31, 20194,253 $29.59 6.8$96,524 
Granted1,647 $27.41 
Exercised(274)$16.06 
Canceled(315)$38.00 
Outstanding at December 31, 20205,311 $29.12 7.1$14,131 
Exercisable at December 31, 20203,061 $25.08 5.8$13,515 
Schedule of Restricted Stock Units Activity
The following table summarizes the Company’s restricted stock unit activity for 2020:
Shares
(in thousands)
Weighted Average Fair Value per RSU at Grant Date
Nonvested at December 31, 2019439 $36.97 
Granted218 $27.34 
Vested(220)$26.39 
Canceled(44)$38.15 
Nonvested at December 31, 2020393 $37.68 
Assumptions used in the Black-Scholes Option-Pricing Model A summary of the assumptions used to estimate the fair values of stock option grants for the years presented is as follows:
 Year Ended December 31,
 202020192018
Risk free interest rate
0.3% to 1.8%
1.4% to 2.6%
2.3% to 3.0%
Expected term
5.3 to 6.1 years
5.3 to 6.1 years
5.3 to 6.1 years
Expected volatility
73.2% to 76.7%
73.5% to 82.3%
80.1% to 85.2%
Expected dividend yield—%—%—%
Weighted-average fair value of option on grant date$17.86$32.64$30.87
Stock-Based Compensation Expense
The following table summarizes the components of total stock-based compensation expense included in the consolidated statements of operations for the periods presented:
 Year Ended December 31,
(In thousands)202020192018
Research and development12,139 8,293 6,317 
Selling, general and administrative17,037 12,954 9,175 
Total$29,176 $21,247 $15,492