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Stockholders' Equity (Tables) | 12 Months Ended
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Dec. 31, 2020
Share-based Payment Arrangement [Abstract] |
Stock-Based Compensation Expense for Employees and Non-Employees | Total share-based compensation expense recorded for employees and non-employees, is as follows (in thousands):
|  |  | Years Ended December 31,
|  |  |  |  | 2020 |  | 2019 |  | 2018
Cost of revenues |  |  |  |  | $ | 950 |  |  | $ | 426 |  |  | $ | 420 |
Research and development |  |  |  |  | 31,588 |  |  | 22,229 |  |  | 17,055 |
Sales and marketing |  |  |  |  | 9,606 |  |  | 7,380 |  |  | 6,703 |
General and administrative |  |  |  |  | 41,911 |  |  | 34,874 |  |  | 27,852 |
Total share-based compensation expense |  |  |  |  | $ | 84,055 |  |  | $ | 64,909 |  |  | $ | 52,030 |
Summary of Assumptions Used to Determine Fair Value of ESPP | The following table summarizes the key assumptions used to determine the fair value of rights granted under the 2013 ESPP:
|  |  | Years Ended December 31,
|  |  |  |  | 2020 |  | 2019 |  | 2018
Expected term (years) |  |  |  |  | 0.50 |  | 0.50 |  | 0.50
Expected volatility |  |  |  |  | 52.06%-68.09% |  | 40.51%-41.81% |  | 42.07%-44.97%
Dividend yield |  |  |  |  | — | % |  | — | % |  | — | %
Risk-free interest rate |  |  |  |  | 0.12%-0.15% |  | 1.59%-2.43% |  | 2.09%-2.50%
Weighted-average grant-date fair value per share |  |  |  |  | $ | 20.52 |  |  | $ | 9.88 |  |  | $ | 7.14 |
Summary of Stock Option Activity | Stock Option Activity
|  |  | Options Outstanding
|  |  | Number of Options Outstanding |  | Weighted- Average Exercise Price per Share |  | Weighted-Average Remaining Contractual Term in Years |  | Aggregate Intrinsic Value
Balance at December 31, 2019 |  |  | 1,611,385 |  |  | $ | 8.64 |  |  | 3.60 |  | $ | 47,171,160 |
Exercised |  |  | (984,068) |  |  | 9.13 |  |  |  |  |
Balance at December 31, 2020 |  |  | 627,317 |  |  | $ | 7.86 |  |  | 3.48 |  | $ | 51,733,285 |
Summary of Restricted Stock Unit Activity | RSU and PSU Activity
| RSUs and PSUs Outstanding
| Number of RSUs and PSUs Outstanding |  | Weighted Average Grant Date Fair Value
Balance at December 31, 2019 | 6,909,530 |  |  | $ | 24.04 |
Granted | 2,593,745 |  |  | 45.37 |
Released | (4,098,742) |  |  | 20.22 |
Canceled | (588,533) |  |  | 31.84 |
Balance at December 31, 2020 | 4,816,000 |  |  | $ | 37.82 |

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- Definition Tabular disclosure of allocation of amount expensed and capitalized for award under share-based payment arrangement to statement of income or comprehensive income and statement of financial position. Includes, but is not limited to, corresponding line item in financial statement. + 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 (h)(1) -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 S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901 + Details
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- Definition Tabular disclosure of the number and weighted-average grant date fair value for restricted stock units that were outstanding at the beginning and end of the year, and the number of restricted stock units that were granted, vested, or forfeited during the year. + 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 (c)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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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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