Financial Instruments and Fair Value - Summary of Contractual Maturities of Investments (Detail) - USD ($) $ in Thousands |
Apr. 30, 2019 |
Jan. 31, 2019 |
|---|---|---|
| Available For Sale Securities Debt Maturities Fair Value [Abstract] | ||
| Due within one year | $ 155,140 | $ 151,991 |
| Due within one to three years | 51,612 | 53,115 |
| Total cash equivalents and marketable debt securities | $ 206,752 | $ 205,106 |