Stock-based Compensation - Additional Information (Detail) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
Oct. 31, 2015 USD ($) $ / shares shares	Oct. 31, 2015 USD ($) $ / shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted restricted stock awards shares \| shares	84,239
Closing price of ordinary shares \| $ / shares	$ 49.44	$ 49.44
Stock options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized compensation cost, stock options	$ 12.4	$ 12.4
Weighted average recognition period		2 years 7 months 2 days
Restricted stock units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized compensation cost, restricted stock units	111.4	$ 111.4
Weighted average recognition period		3 years 3 months 29 days
Restricted Stock Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average recognition period		3 years 10 months 13 days
Total unrecognized compensation cost, restricted stock awards	4.7	$ 4.7
Restricted stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate intrinsic value of unvested restricted stock	$ 132.6	$ 132.6

Closing market price of ordinary shares on NASDAQ on the last day of reporting period.

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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ 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=6415400&loc=d3e5070-113901

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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.

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- Definition

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

+ References

No definition available.

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- Definition

Unrecognized cost of unvested options awarded to employees as compensation.

+ References

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

Intrinsic value of equity-based compensation awards not vested. Excludes stock and unit options.

+ References

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- Definition

Total number of shares issued during the period, including shares forfeited, as a result of Restricted Stock Awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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