Financial Instruments and Fair Value - Schedule of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Jul. 31, 2018	Jan. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	$ 102,553	$ 101,707
Included in cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	21,882	13,788
Included in marketable securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	$ 80,671	$ 87,919