Fair Value Measurements - Schedule of Financial Assets and Liabilities (Details) - USD ($)
$ in Thousands |
Apr. 30, 2019 |
Jan. 31, 2019 |
| Short-term investments: |
|
|
| Total financial assets |
$ 368,702
|
$ 406,154
|
| Level 1 |
|
|
| Short-term investments: |
|
|
| Total financial assets |
368,702
|
406,154
|
| Level 2 |
|
|
| Short-term investments: |
|
|
| Total financial assets |
0
|
0
|
| Level 3 |
|
|
| Short-term investments: |
|
|
| Total financial assets |
0
|
0
|
| U.S. government treasury securities |
|
|
| Short-term investments: |
|
|
| Short-term investments: |
318,346
|
318,139
|
| U.S. government treasury securities | Level 1 |
|
|
| Short-term investments: |
|
|
| Short-term investments: |
318,346
|
318,139
|
| U.S. government treasury securities | Level 2 |
|
|
| Short-term investments: |
|
|
| Short-term investments: |
0
|
0
|
| U.S. government treasury securities | Level 3 |
|
|
| Short-term investments: |
|
|
| Short-term investments: |
0
|
0
|
| Money Market Funds |
|
|
| Cash and cash equivalents: |
|
|
| Cash and cash equivalents: |
50,356
|
88,015
|
| Money Market Funds | Level 1 |
|
|
| Cash and cash equivalents: |
|
|
| Cash and cash equivalents: |
50,356
|
88,015
|
| Money Market Funds | Level 2 |
|
|
| Cash and cash equivalents: |
|
|
| Cash and cash equivalents: |
0
|
0
|
| Money Market Funds | Level 3 |
|
|
| Cash and cash equivalents: |
|
|
| Cash and cash equivalents: |
$ 0
|
$ 0
|