Stock-Based Compensation - Stock options - Assumptions (Details)	6 Months Ended
Jul. 31, 2019	Jul. 31, 2018
Stock options
Assumptions
Expected term (in years)	6 years 18 days	6 years 18 days
Risk-free interest rate	2.00%	2.90%
Expected stock price volatility	37.70%	38.10%
Minimum \| Employee Stock Purchase Plan
Assumptions
Expected term (in years)	6 months
Risk-free interest rate	1.90%
Expected stock price volatility	33.00%
Maximum \| Employee Stock Purchase Plan
Assumptions
Expected term (in years)	2 years
Risk-free interest rate	2.20%
Expected stock price volatility	35.70%

No definition available.

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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.

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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

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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-Name Accounting Standards Codification
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