Fair value of financial assets and liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Fair value of financial assets and liabilities
Transfer from Leve 1 to Level 2, assets	$ 0	$ 0
Transfer from Leve 2 to Level 1, assets	0	0
Transfers into Level 3, assets	0	0
Transfer out of Level 3, assets	0	0
Transfer from Leve 1 to Level 2, liabilities	0	0
Transfer from Leve 2 to Level 1, liabilities	0	0
Transfers into Level 3, liabilities	0	0
Transfer out of Level 3, liabilities	0	0
Recurring
Fair value of financial assets and liabilities
Assets fair value	444,518	145,767
Level 2 \| Recurring
Fair value of financial assets and liabilities
Assets fair value	444,518	145,767
Money market funds \| Recurring
Fair value of financial assets and liabilities
Assets fair value	150,734	36,712
Money market funds \| Level 2 \| Recurring
Fair value of financial assets and liabilities
Assets fair value	150,734	36,712
Commercial paper \| Recurring
Fair value of financial assets and liabilities
Assets fair value		21,884
Commercial paper \| Level 2 \| Recurring
Fair value of financial assets and liabilities
Assets fair value		21,884
US Treasury bonds \| Recurring
Fair value of financial assets and liabilities
Assets fair value	226,772	35,810
US Treasury bonds \| Level 2 \| Recurring
Fair value of financial assets and liabilities
Assets fair value	226,772	35,810
US Government Agency bonds \| Recurring
Fair value of financial assets and liabilities
Assets fair value	67,012	15,295
US Government Agency bonds \| Level 2 \| Recurring
Fair value of financial assets and liabilities
Assets fair value	$ 67,012	15,295
Corporate debt securities \| Recurring
Fair value of financial assets and liabilities
Assets fair value		36,066
Corporate debt securities \| Level 2 \| Recurring
Fair value of financial assets and liabilities
Assets fair value		$ 36,066

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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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.

+ References

No definition available.

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Amount of transfers of liabilities measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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Amount of transfers of liabilities measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Amount of transfers of financial instrument classified as a liability into level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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Amount of transfers of financial instrument classified as a liability out of level 3 of the fair value hierarchy.

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Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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