Income Taxes - Effective Income Tax Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Effective Income Tax Rate Reconciliation, Amount
Income tax expense at Bermuda statutory rate	$ 0	$ 0	$ 0
Foreign rate differential	(40,056)	(31,252)	(14,802)
Impact of changes in enacted income tax rates	(27,150)	0	0
R&D tax credits	(4,224)	0	0
Share-based compensation deferral adjustment	4,089	0	0
Change in uncertain tax positions	3,016	0	0
Valuation allowance	65,193	32,335	13,966
Tax reform	0	0	1,049
Other	(107)	(607)	0
Total income tax expense	$ 761	$ 476	$ 213
Effective Income Tax Rate Reconciliation, Percent
Income tax expense at Bermuda statutory rate	0.00%	0.00%	0.00%
Foreign rate differential	13.90%	11.44%	10.35%
Impact of changes in enacted income tax rates	9.42%	0.00%	0.00%
R&D tax credits	1.47%	0.00%	0.00%
Share-based compensation deferral adjustment	(1.42%)	0.00%	0.00%
Change in uncertain tax positions	(1.05%)	0.00%	0.00%
Valuation allowance	(22.62%)	(11.83%)	(9.77%)
Tax reform	0.00%	0.00%	(0.73%)
Other	0.04%	0.22%	0.00%
Total income tax expense	(0.26%)	(0.17%)	(0.15%)