Income taxes - Summary of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Current tax
Domestic (South Africa)	$ (4,261)	$ (5,620)	$ (3,639)
Foreign federal	0	0	0
Foreign state	(978)	(1,109)	(663)
Total Current	(5,239)	(6,729)	(4,302)
Deferred tax
Domestic (South Africa)	(4,744)	(3,963)	1,221
Foreign federal	55	115	0
Foreign state	99	762	545
Total deferred	(4,590)	(3,086)	1,766
Total income tax expense	$ (9,829)	$ (9,815)	$ (2,536)