Income Tax Rate Reconciliation, Estimated Research Tax Credit Benefit, Amount

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of (increase) decrease reasonably possible in the estimated lower bound of the unrecognized tax benefit for a tax position taken or expected to be taken.

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Amount of (increase) decrease reasonably possible in the estimated upper bound of the unrecognized tax benefit for a tax position taken or expected to be taken.

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Amount of increase (decrease) to previously recorded tax expense. Includes, but is not limited to, significant settlements of income tax disputes, and unusual tax positions or infrequent actions taken by the entity, including tax assessment reversal, and IRS tax settlement.

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Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

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-Name Accounting Standards Codification

-Glossary Unrecognized Tax Benefit

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended	3 Months Ended			12 Months Ended
	Apr. 30, 2015	Apr. 30, 2015	Jan. 31, 2014	Jan. 31, 2015	Apr. 30, 2014	Oct. 31, 2015
Taxes [Line Items]
Statutory federal income tax rate	35.00%	35.00%
Gross unrecognized tax benefits	$ 129.9us-gaap_UnrecognizedTaxBenefits	$ 129.9us-gaap_UnrecognizedTaxBenefits
Unrecognized tax benefits that would affect effective tax rate	129.9	129.9
Estimated potential decrease in underlying unrecognized tax benefits, minimum	0	0
Estimated potential decrease in underlying unrecognized tax benefits, maximum	37	37
Fiscal Year 2012 \| IRS
Taxes [Line Items]
Unrecognized tax benefits decrease resulting from settlement			10.0
Fiscal Year 2012 \| Taiwan
Taxes [Line Items]
Unrecognized tax benefits decrease resulting from settlement				1.1
Fiscal Year 2009 and 2010 \| Taiwan
Taxes [Line Items]
Unrecognized tax benefits decrease resulting from settlement					5.1
Tax Adjustments, Settlements, and Unusual Provisions					3.9
Forecast
Taxes [Line Items]
Expected research tax credit benefit						$ 12.4