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Marketable Securities - Additional Information (Detail) $ in Thousands | 12 Months Ended
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Jan. 31, 2019 USD ($) Security | Jan. 31, 2018 USD ($) Security | Jan. 31, 2017 USD ($)
Schedule of Available-for-sale Securities [Line Items] |  |  |
Sales and maturities of marketable securities | $ 267,072 | $ 243,818 | $ 243,159
Amortization of discounts and premiums, net | $ 1,695 | $ 2,588 | 2,200
Total number of securities with unrealized loss positions within the Company's portfolio | Security | 362 | 336 |
Other ( Expense ) Income, Net |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Net realized gain (loss) | $ (22) | $ (35) | $ (83)

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