Description of offering period.

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Description of offering period resets.

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- Definition

Aggregate number of common shares reserved for future issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

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

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- Definition

Unrecognized cost of unvested options awarded to employees as compensation.

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(iii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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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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- Definition

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

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

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- Definition

Percentage of vesting of share-based compensation awards.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
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- Definition

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	12 Months Ended
	Apr. 30, 2017	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate intrinsic value of exercised options		$ 25.6	$ 26.9	$ 24.8
Aggregate estimated fair value of stock options granted to employees vested		$ 9.0	$ 15.2	$ 16.7
Weighted-average grant date fair value of options granted to employees		$ 7.04	$ 5.77	$ 6.72
Unrecognized stock-based compensation expense related to stock option		$ 11.5
Remaining weighted-average period		2 years 5 months 23 days
Stock options forfeited		910,010	1,425,777
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Remaining weighted-average period		2 years 10 months 2 days
Unrecognized stock-based compensation expense		$ 186.2
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Dividend yield		0.00%	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	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		16,772,606			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		2,202,188
Percentage of eligible compensation allowed to employees to purchase shares at a discount		15.00%
Description of offering period excluding initial offering period		Except for the initial 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		$ 6.3
Dividend yield		0.00%	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%