Short-Term Investments - Schedule of Short-Term Investments (Detail) - USD ($) $ in Thousands	Jul. 31, 2017	Jan. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost	$ 315,742	$ 301,507
Available-for-sale securities, Gross unrealized gains	25	39
Available-for-sale securities, Gross unrealized losses	(342)	(280)
Available-for-sale securities, Estimated fair value	315,425	301,266
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost	24,105	20,729
Available-for-sale securities, Gross unrealized gains		5
Available-for-sale securities, Gross unrealized losses	(17)	(16)
Available-for-sale securities, Estimated fair value	24,088	20,718
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost	17,427	20,567
Available-for-sale securities, Gross unrealized gains	1	4
Available-for-sale securities, Gross unrealized losses	(3)	(1)
Available-for-sale securities, Estimated fair value	17,425	20,570
Corporate notes and bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost	107,660	92,843
Available-for-sale securities, Gross unrealized gains	22	14
Available-for-sale securities, Gross unrealized losses	(68)	(101)
Available-for-sale securities, Estimated fair value	107,614	92,756
U.S. agency obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost	83,939	87,091
Available-for-sale securities, Gross unrealized gains		12
Available-for-sale securities, Gross unrealized losses	(99)	(51)
Available-for-sale securities, Estimated fair value	83,840	87,052
U.S. treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized cost	82,611	80,277
Available-for-sale securities, Gross unrealized gains	2	4
Available-for-sale securities, Gross unrealized losses	(155)	(111)
Available-for-sale securities, Estimated fair value	$ 82,458	$ 80,170

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=82897076&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=82897076&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=75030427&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=82896770&loc=d3e26626-111562

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