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Stock-Based Compensation | 3 Months Ended
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Mar. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] |
Stock-Based Compensation |
7. | Stock-Based Compensation
Stock-based compensation expense was recorded directly to research and development and selling, general and administrative expense as follows (in thousands):
|  | Three Months Ended March 31, |
|  | 2021 |  |  | 2020 |
Research and development |  | $ | 12,221 |  |  | $ | 10,637 |
Selling, general and administrative |  |  | 7,163 |  |  |  | 6,279 |
Total stock-based compensation expense |  | $ | 19,384 |  |  | $ | 16,916 |
The assumptions used to estimate the fair value of stock options granted and purchases under the Company’s 2014 Employee Share Purchase Plan (“ESPP”) using the Black-Scholes option valuation model were as follows:
|  | Three Months Ended March 31, |  |
|  | 2021 |  |  |  | 2020 |  |
Stock Options |  |  |  |  |  |  |  |  |  |
Expected term (in years) |  |  | 5.7 |  |  |  |  | 5.7 |  |
Expected volatility |  |  | 58.8 |  | % |  |  | 68.3 |  | %
Risk-free interest rate |  |  | 0.7 |  | % |  |  | 0.9 |  | %
Expected dividend yield |  |  | — |  |  |  |  | — |  |
Weighted average estimated fair value |  | $ | 27.46 |  |  |  | $ | 17.24 |  |
ESPPs |  |  |  |  |  |  |  |  |  |
Expected term (in years) |  | 0.5 - 2.0 |  |  |  | 0.5 - 2.0 |  |
Expected volatility |  | 47.5 - 64.4 |  | % |  | 49.5 - 57.7 |  | %
Risk-free interest rate |  | 0.1 - 2.2 |  | % |  | 1.5 - 2.9 |  | %
Expected dividend yield |  |  | — |  |  |  |  | — |  |
Weighted average estimated fair value |  | $ | 16.94 |  |  |  | $ | 18.57 |  |

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- Definition The entire disclosure for share-based payment arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -URI http://asc.fasb.org/topic&trid=2228938 + Details
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- References No definition available. + Details
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