Short-term investments (Details) - USD ($) $ in Thousands |
6 Months Ended | 12 Months Ended |
|---|---|---|
Sep. 30, 2018 |
Mar. 31, 2018 |
|
| Short-term investments | ||
| Commercial paper classified within cash equivalents | $ 4,993 | $ 0 |
| Short-term investments | ||
| Short-term investments | ||
| Amortized cost | 124,676 | 44,033 |
| Gross unrealized gains | 1 | 2 |
| Gross unrealized losses | (65) | (67) |
| Fair value | 124,612 | 43,968 |
| Short-term investments | Commercial paper | ||
| Short-term investments | ||
| Amortized cost | 90,104 | 28,028 |
| Gross unrealized gains | 2 | |
| Gross unrealized losses | (46) | (32) |
| Fair value | 90,058 | 27,998 |
| Short-term investments | Corporate debt securities | ||
| Short-term investments | ||
| Amortized cost | 34,572 | 16,005 |
| Gross unrealized gains | 1 | |
| Gross unrealized losses | (19) | (35) |
| Fair value | $ 34,554 | $ 15,970 |