Subsequent events (Details)	3 Months Ended			6 Months Ended
	Sep. 30, 2021 R / shares	Sep. 30, 2021 $ / shares	Sep. 30, 2020 $ / shares	Sep. 30, 2021 R / shares	Sep. 30, 2020 R / shares
Subsequent Events [Abstract]
Dividends declared per share (in ZAR per share) | (per share)	R 0.04	$ 0.3	$ 0.3	R 0.04	R 0.04
Dividends declared per ADS (in ZAR per share)	R 1