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Stock-Based Compensation - Narrative (Details) $ / shares in Units, $ in Thousands |  |  |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 44 Months Ended |  |
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Feb. 23, 2024 shares | Mar. 02, 2023 shares | Jan. 01, 2021 | Jan. 01, 2020 shares | May 31, 2021 $ / shares | Nov. 30, 2020 $ / shares | May 31, 2020 tranche shares | Sep. 30, 2024 USD ($) $ / shares shares | Sep. 30, 2023 USD ($) $ / shares shares | Sep. 30, 2024 USD ($) $ / shares shares | Sep. 30, 2023 USD ($) $ / shares shares | Jun. 30, 2024 USD ($) | Dec. 31, 2023 $ / shares shares | Sep. 30, 2018 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted average grant date fair value, grants in period (in usd per share) | $ / shares |  |  |  |  |  |  |  | $ 19.42 | $ 24.42 | $ 15.35 | $ 22.39 |  |  |
Stock based compensation not recognized, options | $ |  |  |  |  |  |  |  | $ 29,300 |  | $ 29,300 |  |  |  |
Stock based compensation not recognized, period for recognition (in years) |  |  |  |  |  |  |  |  |  | 1 year 10 months 24 days |  |  |  |
Compensation expense | $ |  |  |  |  |  |  |  | 49,769 | $ 21,819 | $ 104,045 | $ 66,439 |  |  |
Granted (in shares) |  |  |  |  |  |  |  |  |  | 478,263 |  |  |  |
Stock options |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercises in period, intrinsic value | $ |  |  |  |  |  |  |  | $ 100 | $ 200 | $ 9,100 | $ 900 |  |  |
Expected dividend yield |  |  |  |  |  |  |  | 0.00% | 0.00% | 0.00% | 0.00% |  |  |
Shares underlying unvested restricted stock units |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock based compensation not recognized, period for recognition (in years) |  |  |  |  |  |  |  |  |  | 2 years |  |  |  |
Stock based compensation not recognized, other than options | $ |  |  |  |  |  |  |  | $ 119,100 |  | $ 119,100 |  |  |  |
Unvested balance (in shares) |  |  |  |  |  |  |  | 4,965,567 |  | 4,965,567 |  |  | 4,346,785 |
Weighted average grant date fair value (in usd per share) | $ / shares |  |  |  |  |  |  |  | $ 32.74 |  | $ 32.74 |  |  | $ 42.63 |
Shares underlying unvested performance-based restricted stock units |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted average grant date fair value, grants in period (in usd per share) | $ / shares |  |  |  |  | $ 148.19 | $ 113.40 |  |  |  |  |  |  |  |
Stock based compensation not recognized, period for recognition (in years) |  |  |  |  |  |  |  |  |  | 1 year 10 months 24 days |  |  |  |
Stock based compensation not recognized, other than options | $ |  |  |  |  |  |  |  | $ 13,900 |  | $ 13,900 |  |  |  |
Weighted-average derivative service period |  |  |  |  | 4 years | 4 years |  |  |  |  |  |  |  |
Additional service period requirement |  |  |  |  |  | 2 years |  |  |  |  |  |  |  |
Market-based stock unit vesting period |  |  |  |  | 6 months | 6 months |  |  |  |  |  |  |  |
Weighted average grant date fair value, Vested in period (in usd per share) | $ / shares |  |  |  |  | $ 148.19 | $ 113.40 |  |  |  |  |  |  |  |
Compensation expense | $ |  |  |  |  |  |  |  | 22,700 | $ 800 | $ 26,300 | $ 1,300 | $ 0 |  |
Cumulative charge | $ |  |  |  |  |  |  |  | $ 23,500 |  |  |  |  |  |
Granted (in shares) |  |  |  |  |  |  |  | 221,347 |  |  |  |  |  |
Total market-based restricted stock units approved and granted (in shares) |  |  |  |  |  |  |  |  |  | 870,268 |  |  |  |
Unvested balance (in shares) |  |  |  |  |  |  |  | 1,291,889 |  | 1,291,889 |  |  | 412,490 |
Weighted average grant date fair value (in usd per share) | $ / shares |  |  |  |  |  |  |  | $ 40.30 |  | $ 40.30 |  |  | $ 91.25 |
Shares underlying unvested performance-based restricted stock units | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted-average derivative service period |  |  |  |  |  | 7 months 6 days |  |  |  |  |  |  |  |
Market-based stock unit vesting period |  |  |  |  |  | 7 months 6 days |  |  |  |  |  |  |  |
Shares underlying unvested performance-based restricted stock units | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted-average derivative service period |  |  |  |  |  | 4 years |  |  |  |  |  |  |  |
Market-based stock unit vesting period |  |  |  |  |  | 4 years 6 months |  |  |  |  |  |  |  |
MSUs |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Market-based restricted stock share price goal |  |  | 30 days |  |  |  |  |  |  |  |  |  |  |
Unvested balance (in shares) |  |  |  |  |  |  |  |  |  |  |  |  | 2,260,764 |
Weighted average grant date fair value (in usd per share) | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  | $ 65.20 |
MSUs | Chief Executive Officer |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total market-based restricted stock units approved and granted (in shares) |  |  |  |  |  |  | 1,695,574 |  |  |  |  |  |  |
Number of tranches | tranche |  |  |  |  |  |  | 3 |  |  |  |  |  |  |
Shares available for issuance under the 2018 Employee Stock Purchase Plan |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock based compensation not recognized, period for recognition (in years) |  |  |  |  |  |  |  |  |  | 1 month 6 days |  |  |  |
Stock based compensation not recognized, other than options | $ |  |  |  |  |  |  |  | $ 500 |  | $ 500 |  |  |  |
Compensation expense | $ |  |  |  |  |  |  |  | $ 900 | $ 800 | $ 3,400 | $ 3,800 |  |  |
Expected dividend yield |  |  |  |  |  |  |  |  |  | 0.00% | 0.00% |  |  |
Shares authorized (in shares) | 1,106,700 | 1,026,194 |  | 942,614 |  |  |  |  |  |  |  |  |  |
Maximum employee subscription rate, ESPP |  |  |  |  |  |  |  | 10.00% |  | 10.00% |  |  |  |
Purchase price of common stock (as a percent of the fair value of common stock) |  |  |  |  |  |  |  |  |  | 85.00% |  |  |  |
Purchase period |  |  |  |  |  |  |  |  |  | 6 months |  |  |  |
Common stock issued under employee stock purchase plan (in shares) |  |  |  |  |  |  |  | 0 | 0 | 371,826 | 298,781 |  |  |
Shares available for issuance under the 2018 Employee Stock Purchase Plan | 2018 Employee Stock Purchase Plan |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares approved (in share) |  |  |  |  |  |  |  |  |  |  |  |  |  | 922,250

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