Summary of significant accounting policies (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Summary of significant accounting policies
Cash equivalents	$ 36,712	$ 10,664
Restricted cash	1,636	1,186
Deferred offering costs		2,157
Research and Development Incentives Income	3,084	2,528	$ 2,267
Research and Development Incentives Receivable, Current	2,962	2,474
Foreign currency translation gain (loss)	(236)	(897)	2,376
Net unrealized gain (loss) on short-term investments, net of tax	$ 309	80	$ (65)
Minimum percentage of benefit recognized is being realized upon ultimate settlement	50.00%
Office equipment
Summary of significant accounting policies
Property, Plant and Equipment, Useful Life	5 years
Computer equipment
Summary of significant accounting policies
Property, Plant and Equipment, Useful Life	3 years
Plant, plant and laboratory equipment
Summary of significant accounting policies
Property, Plant and Equipment, Useful Life	5 years
Leasehold improvements
Summary of significant accounting policies
Property, Plant and Equipment, Useful Life	10 years
United Kingdom | Maximum
Summary of significant accounting policies
Percentage of qualifying research and development expenses reimbursed by government	14.50%
Operating Lease [Member]
Summary of significant accounting policies
Restricted cash	$ 1,636	$ 1,186