Stock-based compensation - Classification of expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-Based Compensation
Share-based Compensation	$ 2,801	$ 1,781	$ 5,269	$ 3,591
Total unrecognized compensation cost	29,049		$ 29,049
Expenses expected to be recognized over a weighted average remaining period			2 years 11 months 16 days
Research and development expenses
Share-Based Compensation
Share-based Compensation	1,298	815	$ 2,297	1,656
General and administrative expenses
Share-Based Compensation
Share-based Compensation	$ 1,503	$ 966	$ 2,972	$ 1,935

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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- Definition

Amount of noncash expense for share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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