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Marketable Securities - Additional Information (Detail) $ in Thousands	12 Months Ended
	Jan. 31, 2020 USD ($) Security	Jan. 31, 2019 USD ($) Security	Jan. 31, 2018 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Sales and maturities of marketable securities	$ 428,508	$ 267,072	$ 243,818
Amortization of discounts and premiums, net	$ 706	$ 1,695	2,588
Total number of securities with unrealized loss positions within the Company's portfolio | Security	83	362
Interest income
Schedule of Available-for-sale Securities [Line Items]
Net realized gain (loss)	$ 39	$ (22)	$ (35)

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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 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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