Commitments and contingencies - Additional information related to leases (Details) $ in Thousands	12 Months Ended
	Mar. 31, 2020 USD ($)
Leases
Right-to-use operating lease asset	$ 4,425
Right-to-use financing lease asset	46,925
Total lease assets	51,350
Operating lease liabilities, current	873
Finance lease liabilities, current	2,411
Operating lease liabilities, non-current	3,737
Finance lease liabilities, non-current	24,967
Total lease liabilities	31,988
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	747
Operating cash flows from finance leases	1,185
Financing cash flows from finance leases	59
Right-to-use asset obtained in exchange for new operating lease liabilities	5,152
Right-to-use asset obtained in exchange for new financing lease liabilities	$ 48,224
Weighted-average remaining lease term - operating leases	8 years 8 months 12 days
Weighted-average remaining lease term - financing leases	19 years 3 months 18 days
Weighted-average discount rate - operating leases	7.00%
Weighted-average discount rate - financing leases	8.00%