Financial Instruments and Fair Value - Schedule of Cash Equivalents and Marketable Debt Securities (Detail) - USD ($) $ in Thousands	Jan. 31, 2020	Jan. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable debt securities	$ 211,081	$ 205,106
Included in cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable debt securities	37,736	40,245
Included in marketable debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable debt securities	$ 173,345	$ 164,861