Stock-based compensation - Changes in company RSU (Details) $ / shares in Units, $ in Millions	12 Months Ended
Mar. 31, 2021 USD ($) $ / shares shares
Number of Restricted Shares
Ending balance (in shares) \| shares	15,975
Weighted Average Grant Date Fair Value
Ending balance (in dollars per share) \| $ / shares	$ 34.15
Weighted-average period	3 years
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	4 years
Number of Restricted Shares
Granted (in shares) \| shares	15,975
Weighted Average Grant Date Fair Value
Granted (in dollars per share) \| $ / shares	$ 34.15
Unrecognized compensation cost \| $	$ 0.5
Weighted-average period	3 years 10 months 24 days

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

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-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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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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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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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.

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