Stock-based compensation plan - Summary of Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Share-based Payment Arrangement [Abstract]
Number of Options, Outstanding (in shares)	3,500,000	3,500,000
Weighted Average Exercise Price, Outstanding (in dollars per share)	$ 0.23	$ 0.23
Weighted Average Remaining Contractual Term, Outstanding	5 months 12 days
Aggregate Intrinsic Value, Outstanding	$ 385
Vested:
Number of Options, Vested (in shares)	3,500,000
Weighted-Average Exercise Price, Vested (in dollars per share)	$ 0.23
Weighted Average Remaining Contractual Term, Vested	5 months 12 days
Aggregate Intrinsic Value, Vested	$ 385

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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