Income Taxes - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Income Tax Disclosure [Abstract]
Provision (benefit) for income taxes	$ 12,717	$ (205,339)	$ (1,039)	$ (206,943)
Pretax income (loss)	30,453	$ 24,283	$ 7,490	$ 61,438
Effective negative tax rate			14.00%	337.00%
Discrete tax benefit from partial release of valuation allowance				$ 265,700
Income tax benefit recognized from stock compensation expense			$ 138,600	$ 103,800
Reasonably possible decrease of unrecognized tax benefits	$ 9,000		$ 9,000

Amount of decrease reasonably possible in the next twelve months for the unrecognized tax benefit.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (d)(3)
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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to increase (decrease) in the valuation allowance for deferred tax assets.

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