Financial Instruments And Fair Value - Schedule Of Unrealized Losses Were In Continuous Position In Less Than Twelve Months (Detail) - USD ($) $ in Thousands	Jul. 31, 2020	Jan. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable debt securities	$ 214,016	$ 211,081
Included in cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable debt securities	23,960	37,736
Included in marketable debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable debt securities	$ 190,056	$ 173,345