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Marketable Securities - Additional Information (Detail) $ in Thousands	12 Months Ended
	Jan. 31, 2017 USD ($) Securities	Jan. 31, 2016 USD ($) Securities	Jan. 31, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales and maturities of available-for-sale securities	$ 243,159	$ 374,057	$ 830,297
Amortization of discounts and premiums, net	$ 2,200	$ 3,841	6,696
Total number of securities with unrealized loss positions within the Company's portfolio | Securities	206	84
Other Income ( Expense ), Net
Schedule of Available-for-sale Securities [Line Items]
Net realized gain (loss)	$ (83)	$ 43	$ 237

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

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+ References

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

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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.

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