Financial Instruments and Fair Value - Schedule of Available-for-Sale Securities at Fair Value (Detail) - USD ($) $ in Thousands	Oct. 31, 2017	Jan. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 101,666	$ 100,920
Unrealized Gains	0	13
Unrealized Losses	(116)	(83)
Fair Value	101,550	100,850
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,215	8,328
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	8,215	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	3,499	4,784
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	3,499	4,784
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	52,554	42,713
Unrealized Gains	0	6
Unrealized Losses	(76)	(41)
Fair Value	52,478	42,678
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,708	11,686
Unrealized Gains	0	1
Unrealized Losses	(10)	(12)
Fair Value	10,698	11,675
U.S. government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	26,690	23,409
Unrealized Gains	0	6
Unrealized Losses	(30)	(30)
Fair Value	$ 26,660	$ 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)
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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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