Equity Incentive Plans - Summary of Fair Value of ESPP Estimated Using Black-Scholes Option Pricing Model Assumptions (Details) - $ / shares	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility, minimum		40.00%
Volatility, maximum		43.00%
Volatility	40.00%
Expected term	6 years	6 years
Risk-free interest rate, minimum	2.55%	2.02%
Risk-free interest rate, maximum	3.06%	2.20%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of common stock	$ 16.86	$ 13.84
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of common stock	$ 42.21	$ 15.06
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility	40.00%
Expected term	6 months
Risk-free interest rate, minimum	2.90%
Risk-free interest rate, maximum	2.96%
2018 Employee Stock Purchase Plan \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of common stock	$ 24.00
2018 Employee Stock Purchase Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of common stock	$ 38.18

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The estimated measure of the maximum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

No definition available.

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The estimated measure of the minimum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

No definition available.

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- Definition

The maximum risk-free interest rate assumption that is used in valuing an option on its own shares.

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No definition available.

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The minimum risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Price of a single share of a number of saleable stocks of a company.

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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