Description of offering period.

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Description of offering period resets.

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Aggregate number of common shares reserved for future issuance.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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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.

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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Unrecognized cost of unvested options awarded to employees as compensation.

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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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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No definition available.

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The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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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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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Net number of share options (or share units) granted during the period.

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-Publisher FASB
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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Number of share instruments newly issued under a share-based compensation plan.

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Percentage of vesting of share-based compensation awards.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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

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No definition available.

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Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		3 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2018	Oct. 31, 2017	Apr. 30, 2017	Jan. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate intrinsic value of exercised options			$ 9.4		$ 6.6
Aggregate estimated fair value of stock options granted to employees vested			$ 2.5		$ 2.6
Weighted-average grant date fair value of options granted to employees			$ 7.92		$ 6.74
Unrecognized stock-based compensation expense related to stock option	$ 13.2		$ 13.2
Remaining weighted-average period			2 years 11 months 12 days
Stock options forfeited			283,185
Stock option grants awarded			0
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Remaining weighted-average period			3 years 1 month 24 days
Unrecognized stock-based compensation expense	$ 260.0		$ 260.0
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Dividend yield			0.00%		0.00%
2015 Equity Incentive Plan \| Performance-Based Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted	650,000	475,000
Stock options forfeited				250,000
2015 Equity Incentive Plan \| Class A Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares common stock reserved for issuance	19,511,725		19,511,725			12,200,000
2015 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares common stock reserved for issuance	2,571,580		2,571,580
Percentage of eligible compensation allowed to employees to purchase shares at a discount	15.00%		15.00%
Description of offering period			The 2015 ESPP provides for 24-month offering periods beginning March 16 and September 16 of each year, and each offering period consists of four six-month purchase periods.
Purchase price of common stock, percentage			85.00%
Description of offering period resets			the offering period resets and the new lower price becomes the new offering price for a new 24 month offering period.
Unrecognized stock-based compensation expense	$ 13.0		$ 13.0
Dividend yield			0.00%		0.00%
2015 Employee Stock Purchase Plan \| Class A Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares common stock reserved for issuance						2,500,000
Vesting Commencement Per Year \| 2015 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options and restricted stock units vesting percentage			25.00%
Vesting Commencement Per Month
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options and restricted stock units vesting percentage			2.08%
Vesting Commencement Per Quarter
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options and restricted stock units vesting percentage			6.25%