Short-Term Investments - Schedule of Short-Term Investments (Detail) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	$ 268,528	$ 25,610
Available-for-sale securities, Gross Unrealized Gains	118	16
Available-for-sale securities, Gross Unrealized Losses	(26)	(1)
Available-for-sale securities, Estimated Fair Value	268,620	25,625
Asset backed-securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	9,323
Available-for-sale securities, Gross Unrealized Losses	(4)
Available-for-sale securities, Estimated Fair Value	9,319
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	3,394
Available-for-sale securities, Estimated Fair Value	3,394
Corporate notes and bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	45,990	10,499
Available-for-sale securities, Gross Unrealized Gains	18	9
Available-for-sale securities, Gross Unrealized Losses	(19)	(1)
Available-for-sale securities, Estimated Fair Value	45,989	10,507
U.S. agency obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	199,822	15,111
Available-for-sale securities, Gross Unrealized Gains	92	7
Available-for-sale securities, Gross Unrealized Losses	(3)
Available-for-sale securities, Estimated Fair Value	199,911	15,118
U.S. treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	9,999
Available-for-sale securities, Gross Unrealized Gains	8
Available-for-sale securities, Estimated Fair Value	$ 10,007

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Section 50

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

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Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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