Equity Incentive Plans - Additional Information (Details)	9 Months Ended
Sep. 30, 2018 shares
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Ordinary shares available for grants	2,223,319
Shares issued under plan	314,207
2015 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Ordinary shares available for grants	10,207,157
2015 Plan \| Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock awards granted, vesting period	4 years
Stock awards granted, expiration period	10 years
2015 Plan \| RSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock awards granted, vesting period	3 years

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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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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Number of shares issued during the period as a result of an employee stock purchase plan.

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