Financial Instruments and Fair Value - Schedule of Available-for-Sale Securities at Fair Value (Detail) - USD ($) $ in Thousands	Jan. 31, 2017	Jan. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 100,920	$ 40,374
Unrealized Gains	13	11
Unrealized Losses	(83)	(18)
Fair Value	100,850	40,367
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,328	530
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	8,328	530
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	4,784	2,598
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	4,784	2,598
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	42,713	21,342
Unrealized Gains	6	7
Unrealized Losses	(41)	(9)
Fair Value	42,678	21,340
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,686	4,586
Unrealized Gains	1	0
Unrealized Losses	(12)	(1)
Fair Value	11,675	4,585
U.S. government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,409	9,274
Unrealized Gains	6	4
Unrealized Losses	(30)	(6)
Fair Value	$ 23,385	9,272
Agency bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,044
Unrealized Gains		0
Unrealized Losses		(2)
Fair Value		$ 2,042

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.

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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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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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