Income Taxes - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Apr. 01, 2017
Income Tax Contingency [Line Items]
U.S. statutory federal income tax rate, percent	35.00%	21.00%	31.60%
Cumulative effect adjustment related to unrecognized excess tax benefits on share based compensation				$ 58,700,000
Valuation allowance		$ 33,499,000	$ 29,049,000
Impact on effective tax rate		61,200,000
Accrued interest or penalties associated with uncertain tax positions		0	0
Income tax expense			$ 5,300,000
United States [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards		$ 761,500,000
Operating loss carryforwards expiration beginning year		2021
United States [Member] | Earliest Tax Year [Member]
Income Tax Contingency [Line Items]
Tax years subject to examination		2016
United States [Member] | Latest Tax Year [Member]
Income Tax Contingency [Line Items]
Tax years subject to examination		2018
United States [Member] | Research [Member]
Income Tax Contingency [Line Items]
Tax credit carryforward amount		$ 163,500,000
United States [Member] | Research [Member] | Earliest Tax Year [Member]
Income Tax Contingency [Line Items]
Tax credit carryforwards expiration beginning year		2026
State [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards		$ 585,100,000
Operating loss carryforwards expiration beginning year		2020
State [Member] | Earliest Tax Year [Member]
Income Tax Contingency [Line Items]
Tax years subject to examination		2015
State [Member] | Latest Tax Year [Member]
Income Tax Contingency [Line Items]
Tax years subject to examination		2018
State [Member] | Research [Member]
Income Tax Contingency [Line Items]
Tax credit carryforward amount		$ 146,300,000
State [Member] | Research [Member] | Earliest Tax Year [Member]
Income Tax Contingency [Line Items]
Tax credit carryforwards expiration beginning year		2020
Foreign [Member]
Income Tax Contingency [Line Items]
Tax credit carryforward amount		$ 1,600,000
Foreign [Member] | Earliest Tax Year [Member]
Income Tax Contingency [Line Items]
Tax credit carryforwards expiration beginning year		2021
Tax years subject to examination		2015
Foreign [Member] | Latest Tax Year [Member]
Income Tax Contingency [Line Items]
Tax years subject to examination		2018