Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2023	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Income Tax Contingency [Line Items]
Valuation allowance		$ 353,642	$ 150,047
Valuation allowance	$ 69,000
Impact on effective tax rate		16,100
Accrued interest or penalties associated with uncertain tax positions		2,000	1,100	$ 1,200
Accrued interest and penalties		16,900	16,900
Inmarsat Holdings [Member]
Income Tax Contingency [Line Items]
Accrued interest and penalties recorded as part of the acquisition		19,200
Deferred Tax Asset Valuation Allowance [Member]
Income Tax Contingency [Line Items]
Valuation allowance		139,687	$ 71,976	$ 5,119
United States [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards		$ 345,800
Operating loss carryforwards expiration beginning year		2029
Research and development expenditures, amortization period			5 years
Tax years subject to examination		2021 and thereafter
United States [Member] | Research & Development [Member]
Income Tax Contingency [Line Items]
Tax credit carryforward amount		$ 115,800
United States [Member] | Research & Development [Member] | Earliest Tax Year [Member]
Income Tax Contingency [Line Items]
Tax credit carryforwards expiration beginning year		2040
State [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards		$ 149,000
Operating loss carryforwards expiration beginning year		2025
Tax years subject to examination		2021 and thereafter
State [Member] | Research & Development [Member]
Income Tax Contingency [Line Items]
Tax credit carryforward amount		$ 191,500
State [Member] | Research & Development [Member] | Earliest Tax Year [Member]
Income Tax Contingency [Line Items]
Tax credit carryforwards expiration beginning year		2026
Foreign [Member]
Income Tax Contingency [Line Items]
Research and development expenditures, amortization period			15 years
Tax years subject to examination		2020 and thereafter