Income taxes - Reconciliation of Income Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Income before income tax expense	$ 13,365	$ 17,229	$ 20,816
Tax at South African statutory rate of 28%	3,742	4,824	5,828
Tax effect of:
– Income not subject to tax	(55)	(35)	0
– Non-deductible expenses	626	929	235
– Non-deductible/(non-taxable) foreign exchange movements	(419)	(3,401)	4,085
– Investment in subsidiaries	202	217	42
– Withholding tax	113	23	0
– Utilization of previously unrecognized tax losses	53	(252)	(195)
– Foreign tax paid	357	425	623
– Foreign tax rate differential	(115)	(241)	(213)
– Recognition of previously unrecognized tax losses	35	(73)	(11)
– Tax losses not recognized	314	92	75
– Under-provision prior years	(102)	298	138
– Tax incentives in addition to cost incurred	(253)	(321)	(897)
– Transfer pricing imputation	67	21	65
- Tax rate change	(226)	0	0
– Imputation of controlled foreign company income	83	100	119
– Other	(4)	28	(65)
Income tax expense	$ 4,418	$ 2,634	9,829
Tax benefit recorded that previously was not considered probable			$ 500