Financial Instruments and Fair Value - Schedule of Available-for-Sale Securities at Fair Value (Detail) - USD ($) $ in Thousands	Jul. 31, 2017	Jan. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 101,391	$ 100,920
Unrealized Gains	3	13
Unrealized Losses	(85)	(83)
Fair Value	101,309	100,850
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,232	8,328
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	10,232	8,328
Demand deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		10,000
Unrealized Gains		0
Unrealized Losses		0
Fair Value		10,000
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,980	4,784
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	6,980	4,784
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	48,758	42,713
Unrealized Gains	3	6
Unrealized Losses	(33)	(41)
Fair Value	48,728	42,678
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,024	11,686
Unrealized Gains	0	1
Unrealized Losses	(7)	(12)
Fair Value	13,017	11,675
U.S. government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,397	23,409
Unrealized Gains	0	6
Unrealized Losses	(45)	(30)
Fair Value	$ 22,352	$ 23,385

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

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

+ References

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+ 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 (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
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-Section 45
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-Name Accounting Standards Codification
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