Financial Instruments and Fair Value - Schedule of Available-for-Sale Securities at Fair Value (Detail) - USD ($) $ in Thousands	Jul. 31, 2018	Jan. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 102,764	$ 101,986
Unrealized Gains	1	0
Unrealized Losses	(212)	(279)
Fair Value	102,553	101,707
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	21,882	13,788
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	21,882	13,788
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,833	5,480
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	20,833	5,480
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	42,545	53,175
Unrealized Gains	1	0
Unrealized Losses	(163)	(196)
Fair Value	42,383	52,979
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,551	11,048
Unrealized Gains	0	0
Unrealized Losses	(49)	(44)
Fair Value	12,502	11,004
U.S. government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,953	18,495
Unrealized Gains	0	0
Unrealized Losses	0	(39)
Fair Value	$ 4,953	$ 18,456

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-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 investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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