Equity Incentive Plans - Summary of Estimate Fair Values (Details) - $ / shares	12 Months Ended
Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Employee Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	0 years	6 years 1 month 6 days	6 years 1 month 6 days
Expected volatility	0.00%	47.00%	44.00%
Risk-free interest rate, minimum			1.30%
Risk-free interest rate, maximum			1.50%
Risk-free interest rate	0.00%	1.90%
Dividend rate	0.00%	0.00%	0.00%
Fair value of common stock (in dollars per share)	$ 0.00	$ 12.84
Employee Stock Options \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of common stock (in dollars per share)			$ 10.37
Employee Stock Options \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of common stock (in dollars per share)			$ 14.52
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	44.00%	35.00%
Expected volatility, maximum	47.00%	39.00%
Expected volatility			41.00%
Risk-free interest rate, minimum	2.00%	90.00%	50.00%
Risk-free interest rate, maximum	2.80%	1.40%	90.00%
Dividend rate	0.00%	0.00%	0.00%
Employee Stock Purchase Plan \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 months	6 months	6 months
Fair value of common stock (in dollars per share)	$ 20.62	$ 10.39	$ 12.36
Employee Stock Purchase Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	2 years	2 years	2 years
Fair value of common stock (in dollars per share)	$ 27.66	$ 14.65	$ 13.72

Agreed-upon price for the exchange of the underlying asset relating to the share-based payment award.

No definition available.

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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

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- Definition

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.

+ References

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

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- Definition

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

+ References

No definition available.

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- Definition

The minimum 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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- 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

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
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-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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