Financial Instruments and Fair Value - Schedule of Cash Equivalents and Marketable Debt Securities (Detail) - USD ($) $ in Thousands	Jul. 31, 2019	Jan. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable debt securities	$ 208,329	$ 205,106
Included in cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable debt securities	55,220	40,245
Included in marketable debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable debt securities	$ 153,109	$ 164,861