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Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jul. 31, 2021 | Jul. 31, 2020 | Jul. 31, 2021 | Jul. 31, 2020
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Sales and maturities of marketable securities |  |  | $ 148,582 | $ 383,056
Amortization of discounts and premiums, net | $ 1,398 | $ 208 | 2,736 | 617
Other (Loss) Income, Net |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Net realized gain (loss) | $ 4 | $ 34 | $ 4 | $ (420)

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