Stock-based compensation plan - Summary of SARs (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Mar. 31, 2022 USD ($) $ / shares shares	Mar. 31, 2022 shares	Mar. 31, 2022 USD ($)	Mar. 31, 2022 R / $	Mar. 31, 2022 $ / R	Mar. 31, 2022 $ / £	Mar. 31, 2021 $ / R	Mar. 31, 2021 $ / £	Mar. 31, 2020 $ / R	Mar. 31, 2020 $ / £
Weighted-Average Exercise Price in U.S. Cents
Exchange rate				14.4916	14.49	0.76	14.92	0.73	17.92	0.81
SARs
Number of SARs
Outstanding as of beginning of period (in shares) | shares	40,567,917
Exercised (in shares) | shares	(9,692,917)
Forfeited (in shares) | shares	(2,028,125)
Outstanding as of end of period (in shares) | shares	40,971,875
Vested and expected to vest (in shares) | shares		39,407,969
Vested (in shares) | shares	9,693,750
Weighted-Average Exercise Price in U.S. Cents
Outstanding as of beginning of period (in dollars per share) | $ / shares	$ 0.38
Exercised (in dollars per share) | $ / shares	0.22
Forfeited (in dollars per share) | $ / shares	0.46
Outstanding as of end of period (in dollars per share) | $ / shares	0.45
Vested and expected to vest (in dollars per share) | $ / shares	0.45
Vested (in dollars per share) | $ / shares	$ 0.35
Weighted Average Remaining Contractual Term, Outstanding	3 years 8 months 23 days
Weighted Average Remaining Contractual Term, Vested and expected to vest	3 years 8 months 15 days
Weighted Average Remaining Contractual Term, Vested	1 year 8 months 12 days
Aggregate Intrinsic Value, Vested and expected to vest | $			$ 2,569
Aggregate Intrinsic Value, Vested | $	$ 1,583
SARs | December 9, 2021
Number of SARs
Granted (in shares) | shares	11,625,000
Weighted-Average Exercise Price in U.S. Cents
Granted (in dollars per share) | $ / shares	$ 0.51
SARs | March 24, 2022
Number of SARs
Granted (in shares) | shares	500,000
Weighted-Average Exercise Price in U.S. Cents
Granted (in dollars per share) | $ / shares	$ 0.50