Commitments and contingencies - Lease agreements (Details) $ in Thousands			1 Months Ended				8 Months Ended	12 Months Ended	28 Months Ended
	Oct. 22, 2019 USD ($) ft²	Aug. 01, 2019 USD ($) ft²	Jun. 30, 2019 USD ($) ft²	Jun. 30, 2018 USD ($) ft² Option	Apr. 30, 2016	Dec. 31, 2015 USD ($)	Dec. 03, 2016 USD ($)	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Apr. 01, 2019 USD ($)
Lease agreements
Number of options to extend lease agreement (in years)						5 years
Monthly lease payments, inclusive of base rent and ancillary charges						$ 7
Prior notice period upon termination of lease					9 months
Base rent of monthly lease payments							$ 23		$ 31
Reclassified from prepaid rent	$ 18,164	$ 2,368
Leased office space | ft²	53,000	10,500	18,700	63,000
Prepaid Rent	$ 261
Lease term			10 years	10 years
Number of options to renewal the lease | Option				2
Renewal period of lease			5 years	5 years
Annual rental payment			$ 488	$ 2,373
Percentage of annual increase in lease rental expenses			1.60%	3.00%
Property, plant and equipment, net								$ 6,860	12,159
Financing obligation									$ (6,561)
Right-to-use asset								4,425
Right-to-use liability			$ 4,363					4,610
ASU 2016-02
Lease agreements
Property, plant and equipment, net										$ 645
Long term prepaid rent										5,006
Right-to-use asset										789
Right-to-use liability										837
ASU 2016-02 | Adjustments
Lease agreements
Property, plant and equipment, net										(11,514)
Financing obligation										6,561
Long term prepaid rent										5,006
Right-to-use asset										789
General and administrative expenses
Lease agreements
Finance Lease Cost								239
Research and development expenses
Lease agreements
Finance Lease Cost								$ 1,034
Build-to-suit lease asset | ASU 2016-02
Lease agreements
Property, plant and equipment, net										$ 11,514