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Marketable Securities - Additional Information (Detail) $ in Thousands	12 Months Ended
	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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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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