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Employee Benefit Plans (Tables) | 12 Months Ended
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Jan. 01, 2021
Share-based Payment Arrangement [Abstract] |
Schedule of Allocated Employee Stock-Based Compensation Expense | We allocated the stock-based compensation expense for our equity incentive plans and our ESPP as follows (in thousands):
| Year Ended December 31,
| 2020 |  | 2019 |  | 2018
Research and development | $ | 37,198 |  |  | $ | 19,374 |  |  | $ | 13,115 |
Selling, general and administrative | 67,872 |  |  | 37,228 |  |  | 27,511 |
Total stock-based compensation expense | $ | 105,070 |  |  | $ | 56,602 |  |  | $ | 40,626 |
| Year Ended December 31,
| 2020 |  | 2019 |  | 2018
Stock options | $ | 19,863 |  |  | $ | 23,422 |  |  | $ | 18,896 |
Restricted stock units | 35,675 |  |  | 26,056 |  |  | 19,569 |
Performance stock units | 47,106 |  |  | 4,878 |  |  | — |
ESPP | 2,426 |  |  | 2,246 |  |  | 2,161 |
Total stock-based compensation expense | $ | 105,070 |  |  | $ | 56,602 |  |  | $ | 40,626 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value | The weighted average grant-date fair value per share of stock options and ESPP purchases were as follows:
| Year Ended December 31,
| 2020 |  | 2019 |  | 2018
Stock options, including PSOs | $ | 9.44 |  |  | $ | 8.19 |  |  | $ | 9.07 |
ESPP | $ | 6.12 |  |  | $ | 4.85 |  |  | $ | 6.40 |
Schedule of Fair Value of Employee Share-Based Payments Awards Stock Option Assumptions and Weighted Average Fair Values | The grant-date fair value of stock option grants, including PSOs, and ESPP purchases was estimated using the following assumptions:
| Year Ended December 31,
| 2020 |  | 2019 |  | 2018
Stock options, including PSOs: |  |  |  |  |
Risk-free interest rate | 0.30 | % |  | 1.77 | % |  | 2.81 | %
Dividend yield | — | % |  | — | % |  | — | %
Volatility | 54 | % |  | 48 | % |  | 55 | %
Expected life | 4.4 years |  | 4.3 years |  | 4.4 years
ESPP: |  |  |  |  |
Risk-free interest rate | 0.79 | % |  | 2.16 | % |  | 1.93 | %
Dividend yield | — | % |  | — | % |  | — | %
Volatility | 52 | % |  | 50 | % |  | 53 | %
Expected life | 6 months |  | 6 months |  | 6 months
Schedule of Fair Value of Employee Share-Based Payments Awards ESPP Assumptions and Weighted Average Fair Values | The grant-date fair value of stock option grants, including PSOs, and ESPP purchases was estimated using the following assumptions:
| Year Ended December 31,
| 2020 |  | 2019 |  | 2018
Stock options, including PSOs: |  |  |  |  |
Risk-free interest rate | 0.30 | % |  | 1.77 | % |  | 2.81 | %
Dividend yield | — | % |  | — | % |  | — | %
Volatility | 54 | % |  | 48 | % |  | 55 | %
Expected life | 4.4 years |  | 4.3 years |  | 4.4 years
ESPP: |  |  |  |  |
Risk-free interest rate | 0.79 | % |  | 2.16 | % |  | 1.93 | %
Dividend yield | — | % |  | — | % |  | — | %
Volatility | 52 | % |  | 50 | % |  | 53 | %
Expected life | 6 months |  | 6 months |  | 6 months
Summary of All Stock Option Activity | Activity for stock options, including PSOs, during the year ended December 31, 2020 was as follows (in thousands, except per share amounts):
| Shares |  | Weighted Average Exercise Price |  | Weighted Average Remaining Contractual Term |  | Aggregate Intrinsic Value
Stock options outstanding at December 31, 2019 | 20,443 |  |  | $ | 9.91 |  |  |  |  |
Granted | 1,637 |  |  | $ | 21.89 |  |  |  |  |
Exercised | (5,633) |  |  | $ | 4.77 |  |  |  |  |
Cancelled | (318) |  |  | $ | 20.12 |  |  |  |  |
Stock options outstanding at December 31, 2020 | 16,129 |  |  | $ | 12.72 |  |  | 3.1 years |  | $ | 131,729 |
Stock options exercisable at December 31, 2020 | 12,656 |  |  | $ | 10.47 |  |  | 2.5 years |  | $ | 128,740 |
Summary of All RSU Activity | Activity for RSUs during the year ended December 31, 2020 was as follows (in thousands, except per share amounts):
| Shares |  | Weighted Average Grant Date Fair Value |  | Weighted Average Remaining Contractual Term |  | Aggregate Intrinsic Value
RSUs outstanding at December 31, 2019 | 4,422 |  |  | $ | 19.30 |  |  |  |  |
Awarded | 3,053 |  |  | $ | 23.49 |  |  |  |  |
Vested and released | (1,699) |  |  | $ | 18.20 |  |  |  |  |
Forfeited | (398) |  |  | $ | 20.25 |  |  |  |  |
RSUs outstanding at December 31, 2020 | 5,378 |  |  | $ | 21.96 |  |  | 1.9 years |  | $ | 107,933 |
Activity for PSUs, during the year ended December 31, 2020 was as follows (in thousands, except per share amounts):
| Shares |  | Weighted Average Grant Date Fair Value |  | Weighted Average Remaining Contractual Term |  | Aggregate Intrinsic Value
PSUs outstanding at December 31, 2019 | 4,379 |  |  | $ | 19.33 |  |  |  |  |
Awarded | 4,656 |  |  | $ | 23.15 |  |  |  |  |
Vested and released | (1,529) |  |  | $ | 19.39 |  |  |  |  |
Forfeited | (128) |  |  | $ | 21.09 |  |  |  |  |
PSUs outstanding at December 31, 2020 | 7,378 |  |  | $ | 21.70 |  |  | 3.5 years |  | $ | 148,076 |

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- Definition Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of employee stock purchase plans, including, but not limited to: (a) expected term, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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