Stock-Based Compensation - Additional Information (Details) $ in Millions	6 Months Ended
Jun. 30, 2019 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense, outstanding stock options	$ 35.7
2018 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares reserved for issuance	5.00%
Shares available for grant (in shares) \| shares	14,790,867
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, stock incentive plans, maximum term	10 years
Estimated remaining weighted average period	2 years 7 months 6 days
Stock options \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock incentive plan, vesting period	3 years
Stock options \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock incentive plan, vesting period	4 years
Restricted shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated remaining weighted average period	1 year 6 months
Unrecognized stock-based compensation expense, unvested restricted stock or RSUs	$ 2.5
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated remaining weighted average period	3 years 4 months 24 days
Unrecognized stock-based compensation expense, unvested restricted stock or RSUs	$ 61.2
Restricted stock units \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock incentive plan, vesting period	2 years
Restricted stock units \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock incentive plan, vesting period	4 years

Common Stock, Capital Shares Reserved For Future Issuance, Annual Increase, Percentage

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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