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Stock-Based Compensation - Narrative (Details) $ / shares in Units, $ in Thousands |  |  | 12 Months Ended
--- | --- | --- | ---
Dec. 05, 2018 USD ($) purchase_period offering shares | Nov. 30, 2018 shares | Dec. 31, 2020 USD ($) installment $ / shares shares | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Aggregate number of shares authorized for issuance (in shares) | shares |  |  | 64,200,000 |  |
Total intrinsic value of options exercised (less than for the year ended December 31, 2017) |  |  | $ 785,700 | $ 75,600 | $ 5,300
Consideration for options exercised |  |  | 179,600 |  |
Restricted stock unit |  |  | 5,000 | 5,500 | 0
Compensation costs |  |  | 93,021 | 81,122 | 72,565
Total unrecognized compensation cost related to non-vested stock-based compensation |  |  | $ 226,800 |  |
Weighted-average period of cost expected to be recognized |  |  | 2 years 10 months 24 days |  |
Service-based awards |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting period |  |  | 4 years |  |
Service-based awards | Twelve months of continued employment or service |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting period |  |  | 12 months |  |
Vesting percentage |  |  | 25.00% |  |
Service-based awards | Following twelve quarters |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting period |  |  | 36 months |  |
Number of installments | installment |  |  | 12 |  |
Stock options |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Aggregate number of shares authorized for issuance (in shares) | shares |  |  | 36,300,000 |  |
Compensation costs |  |  | $ 77,748 | 74,780 | 63,288
Employee stock purchase plan |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Compensation costs |  |  | 2,872 | 1,217 | 0
Performance-based awards |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Compensation costs |  |  | $ 9,600 | $ 9,800 | $ 10,600
2018 Equity Plan |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Aggregate number of shares authorized for issuance (in shares) | shares |  | 13,000,000 |  |  |
Annual percentage increase of shares reserved and available for issuance |  | 4.00% |  |  |
Shares available for future grant (in shares) | shares |  |  | 27,900,000 |  |
2016 Equity Plan | Stock options |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Expiration period |  |  | 10 years |  |
ESPP |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Share available for future issuance (in shares) | shares |  |  | 3,600,000 |  |
ESPP | Employee stock purchase plan |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Aggregate number of shares authorized for issuance (in shares) | shares | 810,000 |  |  |  |
Offering period | offering | 1 |  |  |  |
Purchase period | purchase_period | 1 |  |  |  |
Purchase price at which shares are sold, percent | 85.00% |  |  |  |
Minimum percentage of compensation through payroll deductions | 1.00% |  |  |  |
Maximum percentage of compensation through payroll deductions | 50.00% |  |  |  |
Maximum shares to be purchased during purchase period (in shares) | shares | 3,000 |  |  |  |
Maximum value of shares to be purchased during purchase period | $ 25,000 |  |  |  |
Purchase of common stock under employee stock purchase plan (in shares) | shares |  |  | 251,752 |  |
Weighted average fair value per share (usd per share) | $ / shares |  |  | $ 27.97 |  |
Share-Based Compensation Arrangement By Share-Based Payment Award, Purchase Period | 6 months |  |  |  |
Share-Based Compensation Arrangement By Share-Based Payment Award, Consecutive Offering Period | 6 months |  |  |  |

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