Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2025	Sep. 30, 2023	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2023
Income Tax Contingency [Line Items]
Valuation allowance	$ 430,501		$ 430,501	$ 353,642
Valuation allowance, deferred tax asset, increase	10,300
Valuation allowance		$ 69,000
Impact on effective tax rate	13,600		13,600
Accrued interest or penalties associated with uncertain tax positions	2,500		2,500	2,000	$ 1,100
Accrued interest and penalties	14,400		14,400	16,900
Inmarsat Holdings [Member]
Income Tax Contingency [Line Items]
Accrued interest and penalties recorded as part of the acquisition				$ 19,200
United States [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards	597,200		$ 597,200
Operating loss carryforwards expiration beginning year			2029
Research and development expenditures, amortization period					5 years
Tax years subject to examination			2022 and thereafter
United States [Member] | Research & Development [Member]
Income Tax Contingency [Line Items]
Tax credit carryforward amount	138,400		$ 138,400
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	303,000		$ 303,000
Operating loss carryforwards expiration beginning year			2026
Tax years subject to examination			2022 and thereafter
State [Member] | Research & Development [Member]
Income Tax Contingency [Line Items]
Tax credit carryforward amount	$ 203,400		$ 203,400
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			2021 and thereafter