Revenue recognition - Future performance obligations (Details) - USD ($) $ in Millions	Mar. 31, 2020	Mar. 31, 2019
Transaction Price Allocated to Future Performance Obligations
Amount of transaction price allocated to performance obligations	$ 5.8	$ 5.9
Service-type warranties and research services
Transaction Price Allocated to Future Performance Obligations
Amount of transaction price allocated to performance obligations	5.8
Undelivered licenses of intellectual property
Transaction Price Allocated to Future Performance Obligations
Amount of transaction price allocated to performance obligations	1.7
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-04-01
Transaction Price Allocated to Future Performance Obligations
Amount of transaction price allocated to performance obligations	$ 5.4
Revenue recognition period for remaining performance obligation	12 months

Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130556-203045

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- Definition

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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- Definition

Period in which remaining performance obligation is expected to be recognized as revenue, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130556-203045

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