Financial Instruments and Fair Value - Schedule of Available-for-Sale Securities at Fair Value (Detail) - USD ($) $ in Thousands	Apr. 30, 2018	Jan. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 102,370	$ 101,986
Unrealized Gains	0	0
Unrealized Losses	(389)	(279)
Fair Value	101,981	101,707
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	24,554	13,788
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	24,554	13,788
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,478	5,480
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	5,478	5,480
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	52,848	53,175
Unrealized Gains	0	0
Unrealized Losses	(285)	(196)
Fair Value	52,563	52,979
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,506	11,048
Unrealized Gains	0	0
Unrealized Losses	(74)	(44)
Fair Value	10,432	11,004
U.S. government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,984	18,495
Unrealized Gains	0	0
Unrealized Losses	(30)	(39)
Fair Value	$ 8,954	$ 18,456

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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This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ 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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Amount of debt securities categorized neither as held-to-maturity nor trading.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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