Convertible Senior Notes - Schedule of Interest Expense for the Notes (Details) - Convertible Debt - USD ($) $ in Thousands |
3 Months Ended | |
|---|---|---|
Apr. 30, 2019 |
Apr. 30, 2018 |
|
| Debt Instrument [Line Items] | ||
| Contractual interest expense | $ 563 | $ 0 |
| Amortization of debt discount | 3,033 | 0 |
| Amortization of issuance costs | 188 | 0 |
| Total | $ 3,784 | $ 0 |