Short-Term Investments - Schedule of Short-Term Investments (Detail) - USD ($) $ in Thousands	Jan. 31, 2016	Jan. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	$ 214,113	$ 268,528
Available-for-sale securities, Gross Unrealized Gains	44	118
Available-for-sale securities, Gross Unrealized Losses	(133)	(26)
Available-for-sale securities, Estimated Fair Value	214,024	268,620
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	5,456	9,323
Available-for-sale securities, Gross Unrealized Losses	(2)	(4)
Available-for-sale securities, Estimated Fair Value	5,454	9,319
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	5,970	3,394
Available-for-sale securities, Estimated Fair Value	5,970	3,394
Corporate notes and bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	38,341	45,990
Available-for-sale securities, Gross Unrealized Gains	26	18
Available-for-sale securities, Gross Unrealized Losses	(40)	(19)
Available-for-sale securities, Estimated Fair Value	38,327	45,989
U.S. agency obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	124,626	199,822
Available-for-sale securities, Gross Unrealized Gains	14	92
Available-for-sale securities, Gross Unrealized Losses	(54)	(3)
Available-for-sale securities, Estimated Fair Value	124,586	199,911
U.S. treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	39,720	9,999
Available-for-sale securities, Gross Unrealized Gains	4	8
Available-for-sale securities, Gross Unrealized Losses	(37)
Available-for-sale securities, Estimated Fair Value	$ 39,687	$ 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)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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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
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26626-111562

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