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Marketable Securities - Additional Information (Detail) $ in Thousands	12 Months Ended
	Jan. 31, 2018 USD ($) Security	Jan. 31, 2017 USD ($) Security	Jan. 31, 2016 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Sales and maturities of marketable securities	$ 243,818	$ 243,159	$ 374,057
Amortization of discounts and premiums, net	$ 2,588	$ 2,200	3,841
Total number of securities with unrealized loss positions within the Company's portfolio | Security	336	206
Other ( Expense ) Income, Net
Schedule of Available-for-sale Securities [Line Items]
Net realized gain (loss)	$ (35)	$ (83)	$ 43

X

- Definition

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-Section 45
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-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28541-108399

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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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 9
-Subparagraph (a)
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Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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The cash inflow associated with the sale or maturity (principal being due) of securities not classified as either held-to-maturity securities or trading securities which are classified as available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Section 45
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-Subparagraph (a),(b)
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