Stock Option Plans Stock Option Plans - Fair Value of ESPP Using Black-Scholes (Details) - Shares issuable pursuant to the ESPP	12 Months Ended
Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility (as a percent)	31.90%	38.80%	32.90%
Risk-free interest rate (as a percent)	1.90%	2.40%	1.20%
Expected term (in years)	6 months	6 months	7 months 6 days
Expected dividends (as a percent)	0.00%	0.00%	0.00%

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

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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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No definition available.

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- Definition

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.

+ 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
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-Name Accounting Standards Codification
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-Section S99
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