Earnings per share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Basic earnings per share
Income attributable to ordinary shareholders	$ 10,987	$ 14,810	$ 13,947
Weighted average number of ordinary shares in issue (in shares)	553,653,000	563,578,000	561,088,000
Basic earnings per share (in dollars per share)	$ 0.02	$ 0.03	$ 0.02
Weighted average number of American Depository Shares in issue (in shares)	22,146,000	22,543,000	22,444,000
Basic earnings per American Depository Share (in dollars per share)	$ 0.50	$ 0.66	$ 0.62
Diluted earnings per share
Diluted weighted average number of ordinary shares in issue (in shares)	567,879,000	583,741,000	572,824,000
Diluted earnings per share (in dollars per share)	$ 0.02	$ 0.03	$ 0.02
Diluted weighted average number of American Depository Shares in issue (in shares)	22,715,000	23,350,000	22,913,000
Diluted earnings per American Depository Share (in dollars per share)	$ 0.48	$ 0.63	$ 0.61
Share Appreciation Rights
Diluted earnings per share
Potentially dilutive effect of share-based payment arrangements (in shares)	12,560,000	16,245,000	6,284,000
Options
Diluted earnings per share
Potentially dilutive effect of share-based payment arrangements (in shares)	1,666,000	3,918,000	5,452,000