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Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Sales and maturities of marketable securities			$ 130,029	$ 152,838
Amortization of discounts and premiums, net	$ 517	$ 725	1,151	1,528
Other Income, Net
Schedule of Available-for-sale Securities [Line Items]
Net realized gain (loss)	$ 0	$ (23)	$ (13)	$ (9)

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.

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This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

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Amount of cash inflow from sale, maturity, prepayment and call 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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