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Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Apr. 30, 2020	Apr. 30, 2019
Schedule of Available-for-sale Securities [Line Items]
Sales and maturities of marketable securities	$ 311,258	$ 151,761
Amortization of discounts and premiums, net	409	119
Other Income, Net
Schedule of Available-for-sale Securities [Line Items]
Net realized gain (loss)	$ 454	$ 7

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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Amount of realized gain (loss) on 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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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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