Segment information - Reconciliation of Segment Results to Income Before Tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting [Abstract]
Segment Adjusted EBITDA	$ 44,772	$ 48,811	$ 53,298
Corporate and consolidation entries	(10,243)	(8,879)	(8,366)
Loss contingency	0	0	(233)
Operating lease costs	(1,611)	(1,652)	(1,610)
Product development costs	(1,353)	(1,112)	(1,363)
Depreciation and amortization	(14,951)	(16,559)	(19,972)
Impairment of long-lived assets	(47)	(8)	(6)
Stock-based compensation costs	(1,325)	(1,273)	(660)
Restructuring costs	(164)	(1,055)	1
Net profit/(loss) on sale of property, plant and equipment	36	(13)	270
Net foreign exchange losses	(648)	(959)	(610)
Net interest income/(expense)	(510)	(72)	67
Legal costs associated with patent infringement	(591)	0	0
Income before income tax expense	13,365	17,229	20,816
Segment Reporting Information [Line Items]
Restructuring costs	$ (164)	(1,055)	$ 1
CSO
Segment Reporting Information [Line Items]
Restructuring costs		700
Africa
Segment Reporting Information [Line Items]
Restructuring costs		200
North America
Segment Reporting Information [Line Items]
Restructuring costs		100
Middle East and Australia
Segment Reporting Information [Line Items]
Restructuring costs		$ 100