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Description of purchase price for shares of common stock purchased under employee stock purchase plan.

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Employee stock purchase plan number of shares initially authorized.

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Increase of common stock capital shares reserved for future issuance in each of calendar year.

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Percentage of payroll deduction on eligible compensation.

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Share based compensation arrangement by share based payment award average vesting period.

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Aggregate number of common shares reserved for future issuance.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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Amount of cost to be recognized for option under share-based payment arrangement.

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A description of the time period when the company made its initial offering of a class of securities.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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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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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Number of options outstanding, including both vested and non-vested options.

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Maximum number of shares that may be issued in accordance with the plan as a proportion of outstanding capital stock.

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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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Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Number of non-vested options outstanding.

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Number of options vested.

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Weighted average grant-date fair value of options vested.

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Purchase price of common stock expressed as a percentage of its fair value.

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

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Equity Incentive Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares subject to outstanding awards	5,483,891		5,884,742
Total intrinsic value of options exercised	$ 36.8	$ 109.5
Weighted average grant date fair value of options granted	$ 28.99	$ 17.93
Number of shares, vested	585,475
Number of options unvested	2,486,593
Contractual life	10 years
Expected term	6 years	6 years
Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options, average vesting term	4 years
Expected term	6 years
Non Employee Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options, average vesting term	1 year
Expected term	5 years
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized compensation expense related to stock options	$ 31.9
Unrecognized compensation expense expected to be recognized over weighted average period	2 years 7 months 6 days
Stock Options \| Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting period	4 years
Stock Options \| Non Employee Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting period	1 year
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense expected to be recognized over weighted average period	3 years 6 months
Total unrecognized compensation expense expected to be recognized	$ 123.9
Restricted Stock Units (RSUs) \| Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting period	4 years
Restricted Stock Units (RSUs) \| Non Employee Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting period	1 year
2018 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for issuance	5,315,780
Automatically increase percentage of aggregate number of shares of common stock outstanding	5.00%
Shares subject to outstanding awards	3,540,159
Shares available for future issuance	9,204,822
2006 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares subject to outstanding awards	4,154,956
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for issuance	996,709
Total unrecognized compensation expense related to stock options	$ 1.3
Contractual life	10 years
Expected term	6 months	6 months
Initial offering period	June 15, 2018
Description of offering period for ESPP	The first offering period began on June 15, 2018 and ended on January 31, 2019. Subsequent offering periods begin on August 1 and February 1 (or such other date determined by our Board of Directors or our Compensation and Leadership Development Committee).
Description of purchase price for shares of common stock purchased under ESPP	The purchase price for shares of common stock purchased under the ESPP is 85% of the lesser of the fair market value of the Company’s common stock on (i) the first day of the applicable offering period or (ii) the last day of the purchase period in the applicable offering period.
Percentage of purchase price for shares of common stock under fair value market	85.00%
Employee stock purchase plan number of shares initially authorized	10,102,525
2018 Employee Stock Purchase Plan \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Automatically increase percentage of aggregate number of shares of common stock outstanding	1.00%
Percentage of payroll deduction on eligible compensation	1.00%
Increase of common stock capital shares reserved for future issuance in each of calendar year	1,000,000
2018 Employee Stock Purchase Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of payroll deduction on eligible compensation	15.00%
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for issuance	1,850,081
Common stock, shares purchased	81,894