Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Effective income tax rate	(0.17%)	(0.15%)	0.09%
Operating Loss Carryforwards [Line Items]
Deferred tax assets valuation allowance	$ 92,330	$ 21,367
Switzerland
Operating Loss Carryforwards [Line Items]
Net operating losses	376,200
Ireland
Operating Loss Carryforwards [Line Items]
Net operating losses	32
United Kingdom
Operating Loss Carryforwards [Line Items]
Net operating losses	14,400
United States | Research and Development Credit Carryforward
Operating Loss Carryforwards [Line Items]
Credit carryforwards	$ 7,200