Property, plant and equipment, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2019	Apr. 01, 2019
Property, plant and equipment, net
Property, plant and equipment , gross	$ 7,797	$ 12,563
Less: Accumulated depreciation and amortization	(937)	(404)
Property, plant and equipment , net	6,860	12,159
Depreciation and amortization expense	533	148	$ 109
Financing obligation		(6,561)
ASU 2016-02
Property, plant and equipment, net
Property, plant and equipment , net					$ 645
Long term prepaid rent					5,006
ASU 2016-02 | Adjustments
Property, plant and equipment, net
Property, plant and equipment , net					(11,514)
Financing obligation					6,561
Long term prepaid rent					5,006
Construction in progress
Property, plant and equipment, net
Property, plant and equipment , gross	1,217	124
Plant and laboratory equipment
Property, plant and equipment, net
Property, plant and equipment , gross	3,669	584
Leasehold improvements
Property, plant and equipment, net
Property, plant and equipment , gross	532	154
Computer equipment
Property, plant and equipment, net
Property, plant and equipment , gross	1,658	138
Office equipment
Property, plant and equipment, net
Property, plant and equipment , gross	$ 721	49
Build-to-suit lease asset
Property, plant and equipment, net
Property, plant and equipment , gross		$ 11,514		$ 11,514
Build-to-suit lease asset | ASU 2016-02
Property, plant and equipment, net
Property, plant and equipment , net					$ 11,514