Financial Instruments and Fair Value - Schedule of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Apr. 30, 2018	Jan. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	$ 101,981	$ 101,707
Included in cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	24,554	13,788
Included in marketable securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	$ 77,427	$ 87,919