Employee Benefit Plans \| Performance based restricted stock units (Details) - Performance Shares [Member] - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options	$ 10.6
Nonvested at January 31	170,685
PRSU Granted	153,719	159,148	18,563
PRSU Canceled	31,188
Nonvested at January 31	293,216	170,685
Restricted Stock or Unit Expense	$ 5.8	$ 3.3	$ 0.4
PRSU Weighted-average grant date fair value, non-vested at January 31	$ 89.67
PRSU Weighted-average grant date fair value, Granted	82.13
PRSU Weighted average grant date fair value, Canceled	88.50
PRSU Weighted-average grant date fair value, non-vested at January 31	$ 85.84	$ 89.67
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 8 months
PRSU Weighted-average grant date fair value, Granted		$ 90.95	$ 78.42

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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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-Section 50
-Paragraph 2
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- Definition

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

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The noncash expense that represents the cost of restricted stock or unit distributed to employees as compensation.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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-Publisher FASB
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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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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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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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- Definition

Weighted average grant-date fair value of non-vested options forfeited.

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Weighted average grant-date fair value of non-vested options outstanding.

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