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Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Oct. 31, 2020 | Oct. 31, 2019 | Oct. 31, 2020 | Oct. 31, 2019
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Sales and maturities of marketable securities |  |  | $ 384,999 | $ 382,629
Amortization of discounts and premiums, net | $ 201 | $ 156 | 818 | 427
Other (Loss) Income, Net |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Net realized gain (loss) | $ 1 | $ 6 | $ (419) | $ 32

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