Income taxes (Tables)

12 Months Ended

Mar. 31, 2020

Income taxes

Schedule of net loss before income taxes

	Year Ended March 31,
	2020		2019		2018
United States	$	(12,963)	$	(9,483)	$	(8,992)
Foreign (United Kingdom)		(39,662)		(21,351)		(10,710)
	$	(52,625)	$	(30,834)	$	(19,702)

Schedule of reconciliation of the U.S federal statutory income tax rate

	March 31,
	2020		2019		2018
U.S. Federal statutory income tax rate	(21.00)	%	(21.00)	%	(21.00)	%
State taxes, net of federal benefit	(1.6)		(1.5)		(2.6)
Research and development expenses	2.2		3.1		3.8
Remeasurement of deferred taxes as a result of tax reform	—		—		2.6
Foreign tax rate differential	2.8		2.4		2.2
Change in valuation allowance	16.0		15.5		14.0
Return to provision	1.9		0.4		—
Other	(0.3)		1.1		1.0
Effective income tax rate	0.00	%	0.00	%	0.00	%

Schedule of components of deferred tax assets and liabilities

	March 31,
	2020		2019
Deferred tax assets:
Foreign net operating loss carryforwards	$	9,092	$	4,079
Federal net operating loss carryforwards		2,450		2,223
State net operating loss carryforwards		1,054		684
Property, plant and equipment		5,499		—
Capitalized start-up costs		1,748		1,886
Stock compensation		2,526		573
Accrued expenses		341		1,793
Lease liability		8,705		—
Total deferred tax assets		31,415		11,238
Deferred tax liabilities:
Right-to-use asset		(13,998)		—
Property, plant and equipment		—		(1,842)
Other		(88)		—
Total deferred tax liabilities		(14,086)		(1,842)
Valuation allowance		(17,329)		(9,396)
Net deferred tax assets	$	—	$	—

Schedule of valuation allowance for deferred tax assets

	March 31,
	2020		2019
Valuation allowance as of beginning of year	$	9,396	$	4,724
Increases recorded to income tax provision		8,047		4,672
Decreases recorded to income tax provision for equity		(114)		—
Valuation allowance as of end of year	$	17,329	$	9,396