Commitments and contingencies - Components of lease expense (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended |
|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2019 |
|
| Finance lease costs: | ||
| Amortization of right-of-use asset | $ 607 | $ 666 |
| Interest on lease liabilities | 591 | 652 |
| Operating lease costs | 262 | 633 |
| Total lease cost | $ 1,460 | $ 1,951 |